I spent 15 years with Sprint, 5 with Tmobile and one year with Verizon where I am now. My three children are on ATT with iPhone 4's and they drop calls at an alarming rate. They constantly have problems sending and receiving pictures as well. If you want the best coverage Verizon wins hands down, but you pay dearly for it.
I left T-Mobile for one reason and that was due to a very poor signal at my office where we have a metal roof. My favorite carrier is T-Mobile by a long shot and I would still be there had it not been for that one problem. And yes, I used WiFi calling in my office, but it didn't help texting. I would never consider ATT after seeing my kids problems first hand.
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