Voice calls on slow connection

### Your use case
Imagine I have a super slow mobile internet connection: 64 kbit/s. And I want to make a voice call. Result - almost impossible.

#### What would you like to do?
It'd be nice if we had a fallback to lower bitrate or 8-bit compression of voice calls. Whatsapp can make calls with no problems in this case.

### Have you considered any alternatives?
Only sending messages apply here. Or making a regular phone call.