The equipment that you will need for SIP trunking depends on your current system. If you have an older PBX system, then you may need a SIP-ISDN gateway bod. This acts as a translator between SIP and ISDN of the SIP trunks and PBX system. Individuals and businesses can run SIP trunking over the public internet. However, the quality will be poorer, including time delays and data loss. It is important to have a strong connection when setting up SIP trunks.
Regarding how many SIP trunks are needed, it depends on how many calls the individuals or businesses will be receiving at any give point. For instance, a customer contact center may require a SIP trunk per customer service agent, so that each one could receive simultaneous messages. However, a branch or department that is not so dependent on communication could make do with a SIP trunk per five or six employees.
SIP trunks need to be set up correctly to ensure maximum quality and efficiency, at which point they are more reliable that ISDN. Again, the most important part of SIP trunking is a strong connection – that is the only way to ensure polished and timely communication.
Most likely, SIP trunking will save you money by employing one system for most of your communication.