SIP sends calls over the internet, while a PRI is a copper circuit carriers are retiring.
A PRI was the usual way to connect a PBX, at about two dozen calls per circuit.
Ask whether that copper circuit is still sold at your address.
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A digital circuit that carries around two dozen simultaneous calls over copper. It was the standard way to connect a PBX before SIP, and carriers are retiring it.
A connection that carries calls over the internet to a phone system you already own. It replaces copper lines but keeps your existing PBX.
Yes. Carriers are withdrawing copper services across the country, with notice periods that vary by area. If you are still on a PRI, the migration is a question of when rather than whether.
Usually substantially, because you pay for concurrent calls rather than a fixed circuit. You also stop paying for capacity you do not use, since a PRI is sold in fixed blocks.
If your PBX is recent it may support SIP directly. Older systems need a gateway to translate between the two. An installer can tell you which from the model number.
Related: ucaas-vs-ccaas, call-center-software-for-small-business, business-phone-system-with-call-recording. Glossary: voip, pbx. How to buy.
Data as of 2026-10-04.