FreePBX Call and SIM Call

Hello, I have a big problems with the VoIP call and SIM call. We have made an application for customer service in our resort but we have face some problems while we are on the phone of VoIP and then SIM call calls to this phone when we accept and hold it, we can not hears anything with VoIP call and SIM call. Any solution to solve this problems?

please spend few min to explain call flow from freepbx and SIM and logs here; otherwise, nobody knows your app and “some problems”