Almost every major carrier in the U.S. now has the Palm Centro device, including AT&T, Verizon Wireless, and Sprint (what's up with you T-Mobile?). You can also buy a SIM-unlocked model if you want to use it with T-Mobile or another carrier around the world. I actually purchased a SIM-unlocked model to use with T-Mobile and AT&T and think the Centro is an excellent choice for many people that is priced very well at US$99 with a contract. Palm just announced that they have sold their two-millionth Palm Centro and it is a very successful device for them.
I have recommended the Centro to a few people, primarily those moving from a feature phone to a smartphone, and every single person that has bought one from my recommendation has been very happy with the device and is quite enthusiastic about getting email on the go, doing some basic surfing, and listening to music on their phone. I like the Centro because it is very small and the Palm OS is still the snappiest at switching between applications so it is refreshing for me to use it from time to time.