[TG400] Dispatch incoming GSM calls through the 4 SIMS

Hello,

We're equiped with TG400 and we'd like to know if the following is possible : for now, we have a IPBX connected to our TG400 with a Service provider. When a GSM call is made to the GSM SIM1 card, everything is ok, the call is transmitted to our IPBX, everything works fine.

The problem we have is that we would like to be able to manage up to 4 incoming GSM calls with the following rule : all external phones call the same phone number (GSM1) ; if GSM1 is busy, then the call would use the GSM2 ; if it's busy, then GSM3, and so on.

The goal is to be able to manage up to 4 incoming GSM calls with a "if GSM1 is busy, fallback on GSM2, if it's busy, fallback on GSM3, if it's busy, fallback on GSM4" kind of rule.

My feeling is that the limitation will come from the GSM call forwarding feature, but maybe I'm wrong.

Is that possible?
With best regards,
Gilles BREYSSE