I live next to the water in the San Francisco Bay Area...
and as I'm driving at the top of my street, I get "full bars" and as I pull into my driveway I get 2-3 bars and I end up placing my iPhone in the charger and take all my calls with the iPhone BT, while keeping my iPhone in the EXACT same spot, in order to keep from dropping calls. This is a "tried & tested" way to keep from dropping calls, but recently I've been experiencing more dropped calls in the house, where I have "0 bars" and sometimes "No Service" pops up. I've experienced this same situation with Sprint for almost 10 years, but fewer dropped calls with AT&T. My God, I need to move and give up my home next to the Bay (Coverage map on AT&T website is EXACT for my area)! 😎