You know, T-Mobile charges you less per month if you don't have a contract. Over the course of 2 years, its big enough to pay for a smartphone bought contract free.
I have just done this myself with a 24-month contract saving 6 GBP a month (making it 4 GBP a month, including 500Mb/month of data) which paid for a Milestone 2...
I know that's the case in the US.