Wi-Fi calling will pick up where a bad cell signal leaves off and allow you to make phone calls using your internet connection. To activate it, go to Settings and scroll down to Phone. Then go to "Wi-Fi" calling and turn it on. You may have to enter an address to send to 911 responders when making an emergency calls through Wi-Fi. As soon as it's turned on, you're good to go and - unless your Wi-Fi peters out- your phone should never drop a call again.
This hack only works on iPhones that are 5C model or later, though so if your phone isn't one of these, you may want to invest in a cell signal booster, which you can order through The Apple Core.