A piece of iron GSM-gateway with automatic telephone exchange or WITHOUT automatic telephone exchange?

Question

mobile connection

A small PBX is planned, now we are choosing which GSM gateway to take. With built-in automatic telephone exchange or separately. What do you recommend?
PBX functions:

1. 3 sims
   
2. Incoming / outgoing calls with sim
   
3. receiving sms from numbers \ sending sms from selected sim card number
   
4. Call statistics: Dialed \ Answered \ Missed
   
5. Waiting on the line in case our operator did not have time to pick up the phone
   
6. Setting up internal lines. To receive calls it was possible both on a fixed VoIP phone and on any other device through any VoIP program, and, accordingly, it is possible for several employees to work at once
   

The fundamental principle of setting everything up will be stability. Set once and forget.
If you take a GSM gateway without a PBX, while looking after this one - NeoGate TG400

Answer 1

If you do not plan to use pure mt sms with optional TLVs, then the choice is definitely a piece of iron. It will provide the required functionality + will become the only point of failure (I do not take automatic telephone exchange into account).
With an asterisk, this device is quite tolerably friendly.