Some comparisons AT&T vs t-mobile. Clearly, if you are looking for simple mobile voice solutions and you are "in footprint" t-mobile is a good solution. Here are 4 ways AT&T may be a better choice for some users...
1) Better coverage if you travel. This is especially true if you have a "smartphone/pda" like device. t-mobile has decent 3G coverage in the major cities, but move beyond them, and you quickly find yourself in UTMS territory so the service slows way down.
2) Many of the 3G AT&T phones have integrated wifi capability. This can be very handy if you are inside of a building where the gsm signal has trouble penetrating. Since AT&T supplies most of the wifi access for the most widespread locations (think Starbucks), this can give you access to data where you could not get the phone to work.
3) AT&T is in the process of upgrading it's 3G network. This is not only a software upgrade that boosts the ideal speed over the air to nearly 7mb, but according to Randall Stephenson, also has increased the capacity at the cell sites themselves. So, when the signal gets to the cell site, the site will not be overwhelmed and less likely to slow down.
4) AT&T continues to invest in upgrading its network and offerings. Integration with TV on the phone continues to progress.
If all you need is to make a phone call, t-mobile is a good choice, it is cheap. But more and more, people are looking to add data applications to their devices. As this wireless mobilization of the web continues, the network with the capacity to support these applications will have an increasing edge.