Hello,
The Base HAT doesn’t contain the audio code as a result, you cannot receive or send voice.
However, you will be able to make blank calls, i.e to trigger an event. The phone will ring on the other side.
In order power cycle the Module, you can use GPIO26. This is Power regulator control. Normally pulled-down, when this pin drove to HIGH, Hat’s power will cut off.
We Rock Pi X to replicate your system and test. We can run a test with similar module FW and Raspberry Pi.