I'm trying to understand how SIP works and the industry in general. We are planning to setup a PBX (open source) and have SIP phones for our customer care agents.
When I was researching on SIP trunks, I found that some providers give you a range of numbers with the trunk. This is confusing to me, since I imagined that a SIP trunk was linked to a single phone number on the PSTN and we would manage the SIP numbers internally in the PBX.
Could someone please explain the range of numbers and tell me if I have not understood SIP trunks correctly?