When T-Mobile started their new no-contract flat-rate campaign, it appealed tremendously to me. Even if my options are realistically limited (where else am I supposed to take our phones other than back to AT&T if I were to decide T-Mobile wasn't working out?), I like the no-contract policy. I like that I pay $20/mo (more if I want to drop it faster, though there's no interest being charged) toward the balance on my new phone, and when it's paid, that $20/mo comes off the bill automatically (a basic bit of fair dealing that AT&T never offered). I like not caring about minutes (rollover, night, weekend, mobile-to-mobile, or any other damn kind) - figuring out my phone plan shouldn't be only marginally easier than doing my taxes.
More than anything else, I like that my total monthly bill from T-Mobile is about 30% of I was paying AT&T. There are a couple of "gotchas", but none that I can't live with (so far). Your mileage will vary, depending on where you live and what you expect from your mobile carrier.
Collectively, we have an iPhone 4, a 4S, and a 5 (the 4s were previously AT&T, unlocked via ReleaseMyCode.com and brought over with us - I bought the 5, factory-modified to support their AWS bands, from T-Mobile as part of the switch), using them mostly in/around Corona, CA and to a lesser extent through Orange County/Riverside. SpeedTest results and signal strength values came from the iPhone 5.
Check T-Mobile's signal strength, both voice and data, where you'll be using them most.
Don't just trust anyone's coverage map claims - if at all possible, actually *go* to some of the places where you'd most often be relying on T-Mobile's signals, with one of their phones. Use this tip to view actual signal strength instead of "bars" if you can (http://lifehacker.com/5929546/see-the-actual-signal-strength-on-your-iphone-with-this-quick-tweak). At our home, which I work from, both voice (~90-110db) and data signal are poor to adequate. This doesn't bother me as much as it might otherwise, because I'm mostly on WiFi (and use Skype over that for work). Coverage around the 92882 ZIP is spotty - I see the dreaded 2G "E" (or even, briefly, "No Service") surprisingly often while driving around town, alternating with pretty good 4G coverage (SpeedTest results have varied from 15Mb to 2Mb down). They're supposedly expanding their network, both working with partners and "refarming" existing towers, so I expect this to improve. If I did more driving around (or thought of my phone as, you know, a phone rather than a pocket computer/Internet terminal), I might have stronger feelings on this point.
Do some math on your voice/data/text usage with your current carrier.
Before I went down to talk to T-Mobile, I spent twenty minutes on AT&T's site building a little spreadsheet showing total per-month and six-month average voice/data/SMS usage for all of our phones. One of the reasons we'd stuck with AT&T so long was that we still had "unlimited" data plans carried forward from our original iPhones in 2007 (at $30/mo each). Turns out none of us had gone over 1G in the last six months. Ari and I hadn't even topped 500Mb. And all of us, even Faith, had insane amounts of "rollover" voice minutes banked. When I eventually called AT&T to cancel, they tried to tell me I was throwing away all the "value" in those rollover minutes. If I could transfer/sell them like airline miles, I *might* have bought that argument.
T-Mobile minutes under this plan are unlimited. Period.
T-Mobile includes 500Mb/mo per device as part of the base plan. If you exceed that, you aren't cut off or automatically charged a fee, you're just throttled to Edge speeds until the end of that billing cycle. You can, if you choose, buy another 2G for $10/mo, or get (genuinely) unlimited full-speed data for $20/mo.
I did manage to exceed 500MB my first month, between running a lot of SpeedTests and inadvertently re-downloading a batch of podcasts when I upgraded my phone. Again, since I mostly work from home I just opted to wait out the few days to the end of the billing cycle.
Turns out (no surprise) that Siri is essentially unusable while throttled to Edge speed.
Tethering is included too (drawing on the same data pool), which AT&T both wanted to charge extra for and was using as leverage against long-time customers on those grandfathered unlimited data plans. None of us use it regularly, but it's a nice option to have.
Unlimited SMS is included, too - this was another extra monthly fee on our previous AT&T account.
NEVER TRUST A TELCO.
Even if you weigh it all out and decide not to switch, do yourself a favor. Call your current mobile service provider and tell them you want to cancel. They'll suddenly remember that you're a "valued customer" and be eager to make sure you stay in the fold by offering all sorts of enticements. Odds are they've been taking advantage of you for years (and will go right back to doing it next week), but right now you're holding the stick - use it to knock your bill down a bit.
And if you really *are* canceling, don't let them kick you one last time on your way out the door. Insist that they cancel your service *immediately*, not at the end of your next billing cycle (assuming that you're already all set up with the new carrier). AT&T tried to slip this one by me.
For the moment, I'm reasonably content with T-Mobile. We're paying a *lot* less, under better terms than before. We're getting a bit less in exchange (in terms of consistent signal coverage and strength), but I expect that to improve, and did I mention we're paying 60% less? If (when?) down the line I'm less pleased with T-Mobile, I'll be applying everything I just (re)learned dealing with AT&T to them.
BTW - if you should decide to switch, drop me an email. If I "refer" you to T-Mobile, we can both save a few extra bucks.