What Is a SIP Phone & How Does It Work?

March 12, 2020 9 min read

Julie Bai

Julie Bai

What is a SIP Phone?

SIP, which is short for Session Initiation Protocol, has quickly become the main topic of discussion for businesses and IT departments looking to expand their company’s phone service beyond one location.
Business leaders are rapidly switching to cloud phone service as a way to equip staff with tools needed to communicate effectively. One of the more cost-effective options is to use SIP-based phone systems.
It’s true. Phone services tend to fall to the lower end of expenses with only 6% of the budget allocated for communications according to a recent IT spending analysis from Spiceworks. This slice of the budget also includes other tools such as Slack or Jira, which limits the amount that can be spent on phones themselves.
Let’s break down everything you need to know about upgrading to the best SIP trunk provider.

What is SIP?

Network Diagram of a Hosted PBX and SIP Trunk

Session Initiation Protocol (SIP) is a communication protocol that manages multimedia communication such as video and voice calls. To use SIP, you need a SIP phone that establishes communication over the internet. Unlike traditional phone systems, SIP phones rely on internet technology to make secure and reliable calls.
The SIP protocol enables organizations to have unified communications as it integrates basic phone capabilities with video, email, instant messaging and more. Organizations use a SIP phone if they’re looking for scalability, reliability, and not limited voice calls. With SIP, you can expand into video and instant messaging.
SIP was created in the 90s and later standardized by the Internet Engineering Task Force (IETF). Its design had bold aspirations to reshape the way we communicate. It aimed to provide a signaling protocol that would not only enable phone calls but could also be used for initiating any kind of communication sessions.
It was designed for more than phone calls, including audio and video calls, and even gaming sessions or controlling a coffee maker.

Examples of SIP applications are found in many communication products today. Desk phones, software-based phones, and even online meeting software use SIP. Some organizations have moved towards upgrading their legacy systems with SIP trunk provider to lower costs and add calling capacity.
Related: What Is Session Initiation Protocol (SIP)?

What are the features of a SIP phone?

Visually, a SIP phone typically looks like your common office phone. Beneath the surface, they provide even greater functionality to manage calls. In addition to completing phone calls, SIP phones can place callers on hold and transfer callers to different extensions. SIP phones outperform traditional phones for achieving higher call quality, too.
The differences come from the back-end, which is why so many IT leaders are drawn to this technology.
SIP phones connect to a VoIP phone service without extra hardware or servers. Because SIP phones don’t require the same installation process as traditional phone lines, they are less expensive to maintain.
It makes sense why organizations turn to this technology for their phone service. Loaded with business VoIP features with none of the hassles, it’s a no-brainer.

Top features of a SIP phone:

  • Basic and advanced call forwarding
  • Hold with optional music
  • Conference calling
  • HD phone calls
  • Auto-attendant
  • Call recording
  • Shared call appearance
  • Custom caller ID
  • Mobile and desktop app integration

What is VoIP, and how does it differ from SIP?

According to the FCC, Voice over Internet Protocol is a technology that allows you to make voice calls using a broadband Internet connection instead of a regular (or analog) phone line. SIP stands out from VoIP because it’s one of the widely accepted standards used to facilitate VoIP.
VoIP can exist without SIP, but SIP offers the most compatibility over proprietary online calling software.

Types of SIP phones

SIP phones generally fall into two categories: hard phones and softphones. Both of these offer superior performance over analog phones, but they afford users many distinct benefits. SIP phones can only work with cloud-based phone systems, unlike traditional analog phones.

Hard Phones (Deskphones and Speakerphones)

A hard phone looks like a regular telephone and indeed behaves like one.
Hard phones connect using Ethernet cables and can come in a cordless form. Popular SIP hard phones include Poly, Cisco, Nextiva, and Panasonic. Most of these desk phones offer similar features with a few differences between them.
Not all hard phones are the same. They are classified into basic, intermediate and advanced categories.

  • Basic: Considered as almost a starter VoIP phone, these SIP phones are what you might see used by call center or contact center staff. These phones have a dial pad and can complete internal and external phone calls. These hard phones are budget-friendly and are very easy to use.
  • Intermediate: A step up from basic, intermediate SIP hard phones provide more robust functionality, often including a browsable directory with multiple extensions. Physically, these phones might have a few more buttons for extra VoIP features. These phones are often deployed across the workforce, even sent with employees if they work from home.
  • Advanced: Advanced SIP hard phones can do anything a basic or intermediate phone can do and often feature a full-color display, multiple extensions, Wi-Fi or Bluetooth compatibility. Visually, these phones look more refined and are enjoyed by company executives. There may be fewer physical buttons on these phones because applications can be accessed through the display.

One limitation of hard phones is that they are stationary. Over half of the United States workforce predicted to work remotely over the coming years, businesses are looking into low-cost alternatives for desk phones.
This is where softphones come into play.

Softphones (VoIP apps & Calling Software)

Softphones are applications that provide users with phone service connectivity through software installed on a desktop, laptop, or smartphone. Once your VoIP app is installed, use a headset and microphone for the best calling experience.
A softphone may be installed by administrators or by users in a self-service format. IT leaders considering using softphone technology need to think about their network utilization.
SIP traffic from softphones can’t be easily singled out as compared to other network applications. For those with a mandatory VPN, you will want to complete a VoIP speed test to evaluate the health of your connection.
With VoIP, call quality adapts to changing network conditions automatically such as limited network bandwidth. For frequent softphone users, they might experience shorter battery life on their cell phones. These factors mean that IT leaders have to plan ahead before deploying softphone apps to their employees.
Related: VoIP Basics: The Beginner’s Guide to Mastering VoIP

How SIP-based telephony works

SIP Protocol Network Diagram - Example of a VoIP call

At a technical level, SIP devices operate using relatively straightforward commands. If you listened on the wire, the network traffic would appear similar to typical HTTP traffic to access web pages. As a reminder, everyday users would never need to mess with these commands—they happen automatically.
When a call is made from a SIP phone, the device notifies the SIP server it’s connected to. In this case, a SIP server would be your business VoIP service.
From there, the SIP server initiates contact with another extension or patches the call over to the Public Switched Telephone Network (PSTN). Once the other party answers the phone, the call is established.
During the call, the SIP server and automatically phones negotiate the call quality and status of the call in real-time.
Here’s a diagram of what this SIP interaction would look like:

Benefits of SIP phones

It can be very cost-effective to upgrade to SIP phones no matter the size of your company. Overall, there are several advantages to using SIP phones.

  • You won’t be dependant on your local telephone company for copper lines.
  • Nearly no maintenance or additional configuration unless you want to.
  • Connect all employees together within the business, including remote staff.
  • Take advantage of encryption for increased call security.
  • Cloud-based management of your phone system means instant delivery of features anytime.

Your main use for SIP phones should be identified more than the brand of SIP phone you select. Think through the real-world examples of how your employees use their phones to communicate. Some employees need more powerful phones like a busy receptionist or a prominent business executive.
Even for small businesses, there’s an affordable SIP phone that will help your team communicate more effectively. Forget about frantically looking for a charging cable for your iPhone with 3% of battery remaining. Just pull the call to your desk phone and breathe easier.

Top Business SIP Phones for 2020

To help you through your next telephony technology investment, we have put together a quick comparison guide of the top SIP phones available on the market today. Just a few notes to keep in mind:

  • Mix and match them to your employee’s needs
  • Support and configuration are often included from a SIP provider
  • You have the option of purchasing or leasing (renting)

Basic SIP Phones

Panasonic KX-HDV130

As an entry-level two-line SIP phone, the Panasonic KX-HDV130 is the ideal choice for users that need a reliable device with advanced call handling features, but don’t juggle many calls at the same time.

  • Number of Lines: 2
  • Display Type: Monochrome
  • Screen Size: 2.3″
  • PoE Available: Yes
  • Warranty: 3 years

Poly VVX 150

A high-quality, two-line, SIP phone, the Poly VVX 150 is ideal for home offices or shared/common areas, such as lobbies, hallways and break rooms or for any location that needs simple and reliable voice connectivity.

  • Number of Lines: 2
  • Display Type: Monochrome
  • Screen Size: 2.5″
  • PoE Available: Yes
  • Warranty: 1 year; lifetime when rented

Intermediate SIP Phones

Nextiva X-815

The Nextiva X-815 is a sleek, six-line, color, SIP phone ideal for call-center or office workers. The phone’s interface is clean and well-organized so you’ll handle calls with greater ease and confidence.

  • Number of Lines: 6
  • Display Type: Color LCD
  • Screen Size: 2.8″
  • PoE Available: Yes
    Gig Ethernet Ports: Yes
  • USB Input: 1
  • Expansion Module Connectivity: Yes, up to 3
  • Warranty: 3 years; lifetime when rented

Poly VVX 350

A high-quality, six-line, color, mid-range, SIP phone ideal for call center operators who handle moderate/high volume of calls and for small teams to know which team members are on the phone.

  • Number of Lines: 6 native lines (24 with pagination)
  • Display Type: Color LCD
  • Screen Size: 3.5″
  • PoE Available: Yes
  • Headset Input: RJ-9
  • USB Input(s): 2
  • Bluetooth/Wi-Fi: Yes, both via dongle
  • Warranty: 1 year; lifetime when rented

Advanced SIP Phones

Nextiva X-885

A sleek, twelve-line, color, SIP phone ideal for executives and receptionists. It has a multi-page approach to provide twelve additional programmable keys.

  • Number of Lines: 12
  • Display Type: Color LCD
  • Screen Size: 4.3″
  • PoE Available: Yes
  • Gig Ethernet Ports: Yes
  • USB Input: 1
  • Expansion Module Connectivity: Yes, up to 3
  • Warranty: 3 years; lifetime when rented

Cisco 8841

Cisco’s 8841 business-class, ten-line, SIP phone is ideal for companies that take calls on multiple phone lines, as each line can handle multiple calls. This powerhouse of a business phone is like nothing you’ve ever used before. It won’t disappoint.

  • Number of Lines: 10
  • Display Type: Color LCD
  • Screen Size: 5″
  • PoE Available: Yes
  • Gig Ethernet Ports: Yes
  • Warranty: 1 year; lifetime when rented

Related: 10 Best VoIP Headsets for Your Business for 2020

What about Company PBXs?

Network Diagrams: Hosted PBX SIP Trunking

If your company has a Private Branch Exchange (PBX), you’re likely using a specialized data lines, collectively known as a trunk. Instead of being limited by legacy technology, SIP provides a simple and easy way to voice services for your existing business phone system. This is known as SIP Trunking or a “SIP Trunk.”
One of the primary reasons why businesses use SIP trunking is to handle more outbound and inbound calling capacity at a much lower cost.
Here’s a diagram showing a SIP Trunk in action alongside a hosted PBX:

How to get a business phone number

The process of getting a phone number for your SIP phone begins by signing up with a VoIP provider. You have the option of using your existing phone numbers through a process known as porting. While porting may take a couple of weeks to complete, you can use temporary numbers right away.
Since every SIP phone has a hardware ID assigned, it looks to the service provider to know which numbers it can use. You or your phone service provider can associate SIP phones with any desired phone number that you authorize.
With Nextiva, your SIP phone comes configured out of the box. Simply plug it in and you can begin taking calls right away.

Recommendations for your SIP Phones

As you decide on the equipment you need for your company’s communications needs, consider these best practices.

  • Evaluate the service provider first, then the SIP phone. Your company’s experience is most influenced shaped by the service provider.
  • Research the company’s network infrastructure. Modern, cloud phone systems have multiple points of presence, known as POPs, around your continent for maximum reliability.
  • Plan your needs 18–24 months out. You might have modest needs today, but they will surely expand as your company grows. Create the working environment you want now so it’s not chaos later.

Last, but certainly not least, is the quality of support you have available. Are they available at 9 p.m. at night? How fast do they answer the phone at 10 a.m.? When it comes to your business, you can’t let life pass you by while waiting on hold.
Now that you’ve researched everything about SIP phones, why not check out VoIP phones we have available. Our team fully tests and supports every device to confirm it meets your business needs.

Get a modern phone system loaded with every
feature your business needs. Get your quote today!
Julie Bai


Julie Bai

Julie Bai was a product manager at Nextiva, UCaaS evangelist, no-bull communicator, and translator for people, dog lover, and mother to an adorably active boy.

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