I'm not sure it is "remaining loyal" as much as "being backed into a corner".
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I have my iPhone 4 on T-Mobile. I moved to the US from Canada and had my phone unlocked before I did. Despite not being able to get 3G speeds, I DO get unlimited data, texts, and unlimited calling to US and to my family back home in Canada, all for a prepaid $60 a month. Never dropped a call and I'm not on any sort of contract so when I change countries again, nothing to worry about.
I switched to Sprint because I got a good discount through my work. To be completely honest, I'm thinking about going back to AT&T. Sprint's coverage is really spotty and their 3G data speed is horrible. No wonder why Sprint offers the unlimited data plan...because the rate at which you use their data will take you twice as long because of their SLOW network!
I have a 4G hotspot of their's and its dog meat. It is so unreliable on 3G or 4G. I have had times where on 4G my data speeds for 256 kb/s