Other parts of the letter include a reason why the relationship between you and your current carrier isn't working, and why you are moving on. Finally, you give the reason why you're switching to T-Mobile, and sign your name. You can then take a look at your completed letter and pass it along to your social networks like Facebook, Twitter and Google+. The letter doesn't automatically get sent to your current carrier unless you mail it to them.
We have got to admit that this is another impressive bit of marketing on T-Mobile's part. It's a bit like playing Mad Libs. You can check out a sample letter in the slideshow below.
source: T-Mobile via AndroidCentral