And ATT will send you a FemtoCell (booster) for free if you complain politely about signal strength.

Another option might be to use your WiFi connection for cell phone calls. Don't know about Android or about carriers other than ATT, but my iPhone8 on ATT has a setting for WiFi calling, and it helps a lot in the house. Cell signal strength here is generally poor and I sometimes have no bars on my phone, but the WiFi setting gets around that (mostly). If your WiFi in the house or shop is spotty, you can get a wireless mesh network for the house/shop to boost WiFi. I will probably do that to get better coverage in the garage and yard. I will probably go with the Eero network extenders because they are simple to install and are reputed to work well. Cost is $200 to about $500, depending on how much territory you want to cover.