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Full Version: Phone SIP accounts vs number of SIP trunks
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Good morning.
What is the relationship between the number of SIP trunk lines coming in to a PBX and the number of SIP accounts a phone has? In my business, we are looking into replacing our old digital PBX / eight analog POTS lines with a VOIP PBX (like Asterisk or 3CX) and SIP trunks. I have already made the assumption that we will have eight SIP trunks to replace the 8 POTS lines to maintain the same number of simultaneous incoming/outgoing calls. However, in looking at various IP phones to use with the PBX, they have varying specifications for number of SIP accounts. Some are as low as one, and other (more expensive) phones have upwards of 15 or 16. Do I need the more expensive phones to handle all eight SIP trunks, or will a three SIP account phone work and not limit it to accessing only three of the eight lines? I suspect that it will, since some companies could have hundreds of incoming SIP trunks, yet I have never seen a phone with that many SIP accounts.

Thanks for all your help.

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%.
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