Turning your phone's connection off and then back on is the quickest and easiest way to try and fix your signal woes. If you're moving around from one location to another, toggling Airplane mode ...

You can turn off call forwarding on your iPhone, or turn it on again at any time to receive calls on a different phone.

You can use Wi-Fi calling on your Android or iPhone to make calls using Wi-Fi rather than your cellular network.