Incoming calls problem to Freepbx endpoints

Our endpoints of Freepbx are registered in different Phones.
But after some time when an endpoint is called then asterisk says no one is available but with the same extension we are able to send outgoing calls and the problem is with the incoming calls only.

And if we restart the phone and it re-registers then we start receiving incoming calls.

Kindly advice.

Prakash Singh Chaudhary.

Different phones on same network?
Different phones: what type
Different phones on what system? FreePBX version/Asterisk version.
says no one is available - is that a voice saying that?

Are you saying that you have the same extension configured on more than one endpoint?

Just a shot in the dark, try setting your extensions as Nat = No-RFC3581 and see what happens.