What limits the number of simultaneous conversations via SIP?

Question

Asterisk

Hello!
We are now using a virtual PBX from TTK (there is an 8-port voice gateway) and we have 5 simultaneous lines (500r per line).
We want to give up their equipment, keep the number and take only SIP settings from it.
And raise your Asteriks, or buy your own voice gateway at the very least.
Question: where is the number of simultaneous calls (lines) regulated / limited? On the side of the SIP provider (TTK) or already on our equipment (Asteriks/VoIP gateway)?
The question arose in connection with a dispute with TTK technical support, which says that they will have to pay for each line, regardless of the equipment, and we just want to avoid these costs.

Answer 1

Restrictions on external lines (incoming / outgoing to the outside world) are regulated by the provider. Having set yourself Asterisk in the context of the question, you will be able to talk on internal lines without a limit, external lines will remain as they were.