In general, T-Mobile service plans are cheaper, but you need to see how many devices you own and how many people will share your service to get comparable prices. In my case, I'll be saving about $20 a month for the same amount of data plus unlimited talk and text. (You can see T-Mobile's data plans here.)
Finally, if you're interested in the upcoming iPhone 6, which is expected to be released in September, you probably want wait to switch. If you don't, you have to buy a current phone from T-Mobile and make at least six monthly payments before you can upgrade. Money spent on a phone you buy today will not be credited towards the purchase of a new phone.
I'm waiting for the iPhone 6, and then I'll say goodbye to AT&T...unless someone makes me a better offer.
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