How to set up the choice of a designated number for an outgoing call on an asterisk?

Question

Asterisk

The question is still purely theoretical, there is no equipment yet.
Given: 10 employees, gsm-gateway for 32 sims (most likely GOIP), FreePBX (maybe not).
Task: How to implement a scheme so that when making an outgoing call through a softphone (possibly through a web face, if necessary), the operator can select a number that will be determined when the subscriber receives an incoming call.
At the same time, each operator will have 3 numbers to choose from?
What is the best way to organize such a system? Aster knowledge at the level of FreePBX Elastix settings with a mouse.

Answer 1

The operator before the dialed number specifies the prefix 1, 2 or 3, for example 28(917)123-23-23.

Answer 2

If the operators have multi-channel phones, then you can hang your number on each channel. If single-channel, then a prefix.
Accordingly, depending on the selected number, the call must go through the desired GoIP channel, this, it seems, is configured through the Restricted Dial Plan on each GSM channel.