Our shop is a metal clad building and cell phone reception inside the building is horrible, its an almost perfect Faraday cage. One step out the door and its 4-5 bars, one step inside and nothing...
I was going to have a phone signal booster installed, they cost anywhere from $400 to several $k plus installation. Basically an outside antenna, an amplifier/booster, and an inside antenna. As I was doing some online research into the best one to buy I read an article that explained that all the major carriers (I have AT&T, Scott has Verizon) now have voice over WiFi. You can change a couple settings in your iPhone (and other brands) so that if your cell phone reception drops below a certain level the call will automatically switch over to using the WiFi network you're connected to.
We have a very good WiFi network in our shop. Once Scott and I changed the settings in our iPhones we got perfect telephone communication.
Here is how to do it on an iPhone:
Make phone calls with Wi-Fi when you have little or no cellular coverage.
support.apple.com
Making phone calls over WiFi makes it hard for emergency services to locate you from your phone signal so it will ask you for a location to use for 911 services. My phone auto-filled in my home address location but if you want to have the ambulance roll up somewhere else you can change it.
I figure the hour I spent online learning how to do this saved me $700 or more.
This won't help if you don't have WiFi but if you do it's a good hack. It seems as if there are a lot of places where there is good, even free WiFi but very poor cell phone coverage. This will help that situation for free!