Does it happen often ?
When you cannot receive an incoming call can you emit an outgoing call ?
When you cannot receive an incoming call, wake-up your phone and call it, does it work ?
On the OP3, I had to modify the wake lock time otherwise the phone was not able to wake from a deep sleep : https://github.com/Halium/android_hardware_ril/commit/104191acb7cf431a92740efb3465d40b2cddcfe1
