How cool it would be if carriers in the US were brave enough to compete on service rather than contract. Talk about letting the free market work as it should..wait, first we need a free market. nevermind.
Um, no one is forcing you to get a contract... Everyone is free to get an unlocked GSM device and use it on any carrier they wish.. AT&T and T-Mobile both have prepaid plans that you can use them with.
If you want to use the phone on T-Mobile you would have to get a device that supports its 3G bands, most non-Windows Phone Nokia's are Pentaband...(The Chipset Microsoft requires for Windows Phone does not support pentaband.)
The only downside to going with an unlocked phone is the high upfront costs.
If you want a low upfront cost you have to get a contract... can't have your cake and eat it too...
There is a free market for GSM devices, it's just expensive....
For most people, the #1 requirement they have for a network is "does it work where I Live/Work/Play?" and once they find one that fits them, they tend to stay with it for a long time. This is why most people don't mind getting a contract. They figure the service is good to great, and they have to pay for the service on a monthly basis to begin with, so why not pay a low up front cost for the device, even if it means a contract...
Very few people switch carriers for a device(iphone excluded)...
because Verizon and Sprint use CDMA, and the carrier has to approve the device, I'm not including them in this discussion.