How do you KNOW you have bad cell service? The “bars” displayed on your phone probably mean next to nothing, and if you have a stock (in other words non-rooted) phone you probably have no way of seeing the signal levels from the individual radios on your phone. Five little bars just don’t tell you much.
I’ve personally found that in the absence of me telling the phone otherwise, the bar display usually shows my LTE signal strength. Which honestly, is next-to-useless if I’m somewhere that my Wi-Fi connects, because I use LTE mostly for data. Sure, AT&T’s new HD Voice feature gives you crystal-clear calls over LTE, but that’s kind of a secondary concern if you can’t receive calls at all.
I would rather my phone told me the signal strength of my voice connection, especially when I’m connected to Wi-Fi. There’s a way to do that, but it’s not a great one.
On your phone, the trick is to turn off ALL LTE communication. This is usually a setting called “Cellular Data” and if you turn it off, most of your LTE communications stop. Not all, though– if your phone supports HD-Voice or any other Voice-over-LTE system, you still may be seeing an LTE-inspired display when you look at your phone’s “bars.” Look for a setting saying “Enable LTE” and see if it’s set for Voice, Voice&Data, or Off. On iPhones it’s right under the Cellular Data switch in the Cellular menu.
Because I usually have a 3G-only booster, my bar displays are pretty low in most cases since my phone seems to be measuring LTE. If I turn off all LTE communication, I can tell that my cell booster is doing its job, because I jump from one bar to five in seconds.
I’ve also noticed that actually making a voice call will force your phone to measure voice signal, but then when you’re trying to call it’s usually too late … you either have signal or you don’t.