When the early termination fee appears on your bill, you have to turn it in to T-Mobile for reimbursement. So you actually have to pay that money up front.
You do have to buy a new phone for every line you switch, so that's an expense. And if your credit rating is less than stellar, you'll have to pay more up front for each phone. T-Mobile will ease the pain with a credit for any phone you turn in up to $300.
How much will they pay for your old phone? According to T-Mobile's website, about $100 for an iPhone 4S and about $160 for a Samsung Galaxy. What T-Mobile actually pays will depend on the phone and the condition it's in when you turn it in.
If you're planning to turn in an old phone, Consumer Reports says take care to wipe it clean of personal data with a factory data reset.
Last, choosing your plan. T-Mobile promises "all plans come with unlimited talk, text, and Web." But watch out! With the lower-cost plans you only get so much data before the speeds slow down.
Still, there could be a reason to switch. Consumer Reports crunched the numbers, and in most cases, T-Mobile's rates were cheaper than those from AT&T, Sprint, and Verizon.
If you're wondering how satisfied T-Mobile customers are, the latest survey of Consumer Reports' subscribers found it was one of the better major providers in many cities.