Phone SIP accounts vs number of SIP trunks

[engine411]

Wrong assumption. I used to think that too.

You can have 1 SIP trunk but still have 8 (or more, or less) concurrent calls on that one trunk. Inbound vs. outbound is irrelevant as far as capacity. The SIP trunk provider might limit that, though.

In my 3CX, we have 1 SIP trunk, and the software licensing (NOT the SIP trunk) allows us 8 concurrent calls, whether internal, inbound from the world, or outbound to the world.

I'm not familiar with using multiple SIP accounts on a phone, however. Someone else will need to chime in there. But those accounts are not related to number of SIP trunks that connect to your PBX. My limited understanding is that multiple accounts on a phone are useful when that one phone needs to be its own PBX, in basic terms. If you want the phone to handle multiple SIP trunks to it, rather than the SIP trunks going to a PBX, or if you want the phone to connect to multiple PBX's, then you use accounts on the phone. We use Yealink phones, and Yealink calls this "lines", as in "the T46G has 6 lines". But that's not the same as 6 analog POTS lines.

SIP/VOIP is awesome. Extreme flexibility and much lower cost. With our 3CX, I've reduced my company's monthly cost by roughly 80%.