iPhone 5 is coming to T-Mobile, but with a unique model compared to the other carriers.
No Contract. It will cost $99 upfront (for the base model), then $20 per month for 20 months, so the phone will be "financed" over time and you'll be free to leave or upgrade as long as you pay for the phone's price.
However, the other aspect is the monthly plan, which is $50 for talk, text and 500mb of data. $10 more for 2.5gb of data or $20 more for unlimited data. So, the maximum cost is $70 per month (plus the $20 for the phone).
Overall, that's still less than the other carriers. Either way, you are paying for the phone directly or indirectly.
So, what's the downside? It's probably the network coverage for T-Mobile, BUT that is changing as they are rolling out LTE in 7 initial markets and then across the United States.
Note: If you want a t-shirt like CNET's Brian Tong, see below:
