Call masking is a method to limit the visibility of a caller's phone number to maintain customer privacy. The number masking VoIP feature lets people and companies choose their virtual phone number on an individual or group basis.

Unlike caller ID blocking (*67), call masking can display a different phone number, such as a temporary phone number, on the recipient's phone.

When you mask your number, it may take up to 15 days for some phone service providers to reflect updates.

Call masking works within a company's VoIP phone system to set the outbound phone number for each phone call. Since masking services can be abused, reputable cloud phone systems require proof of ownership before changing the outbound caller ID.

As calls are placed into the telephone network, header information for the call is provided. Generally, the telephone network "trusts" any caller ID that is provided, thus it's ripe for abuse. Technological advancements have now made it possible to authenticate calls — a technique known as STIR/SHAKEN.

Popular uses of phone number masking often involve customer support, e-commerce, or other brief customer conversations.

Examples of a masked call include:

• Setting the outgoing caller ID, so when a customer calls back a number, they are directed to the auto attendant or the main switchboard.
• Sharing the caller ID among a ring group of sales reps dialing into a local area with its area code.
• Individual small business owners can keep their business calls separate from their mobile phone number.
• Ridesharing and food delivery agents use call masking for short-term, temporary phone numbers to function as a proxy between customers and contractors.

Yes, call masking is legal in the United States so long as you are not using the masked number deceptively or maliciously.

47 CFR § 64.1604 - Prohibition on transmission of inaccurate or misleading caller identification information:

"No person or entity in the United States, nor any person or entity outside the United States if the recipient is within the United States, shall, with the intent to defraud, cause harm, or wrongfully obtain anything of value, knowingly cause, directly, or indirectly, any caller identification service to transmit or display misleading or inaccurate caller identification information in connection with any voice service or text messaging service."

VoIP service providers often require proof of ownership of the desired outgoing phone number and the contact information passed along in caller ID.