[Freeswitch-users] Detect answer on FXO device

I have a Grandstream GXW4108 device, connected to a PSTN line and I use it to make outbound calls via freeswitch. The problem I have is that this device sends SIP 200/OK message immediatly after freeswitch INVITE. There is a way to configure freeswitch to detect the answer (with voice detetection?) and propagate the 200/OK message only on answered calls? Thanks Cristian