My Sony Ericsson T6xx whatever phone is totally dying. I liked it for about the first month, then I realized it totally sucked. Interface is slow, and reception is balls.
Fast forward a year, now its physically starting to break, so its time to switch to Cingular and get a new phone. It seems like the front-runners are:

• Refurb Treo 650 ($140)
• Cingular 2125 (HTC 2125) ($200)
• Nokia 6682 ($300)

Treo: The screen is nice, the keyboard is nice, but everyone says PalmOS is dying. If it is dying, I don’t want to buy into it for the next two years. Another plus side is that it can sync with the Mac no problem. The biggest negative here is that Cingular requires you to use the $40/month data connect plan for unlimited data, instead of the nearly identical $20/month MediaNet plan. Given that I use the thing for 2 years, that’s potentially $240 more that I will be paying total.
HTC 2125: Except for the ‘hump’ that it has, people on the web seem to like this one. It has a QVGA screen but vertical, so I don’t lose anything resolution-wise to the treo. It’s gotta keypad instead of a keyboard, and it also has a joystick instead of a rocker pad (I like the rocker pad better). Windows Mobile 5.0. On the Mac, I have to pay $40 to get the Missing Sync that will let me sync with this thing. I don’t know if connecting to the net through bluetooth will work out of the box. One would assume its a standard bluetooth profile so it should just work. Also, this one comes with MediaNet, so over two years, its actually cheaper than the Treo.
Nokia 6682: I only added this one because it has built in iSync, and it also has Symbian which is another non-dying platform. The screen is small, and it doesn’t support EDGE, so it’s probably out. Plus, it’s too expensive. But people seem to be very fond of their Nokia’s.
In general, why aren’t there more flip phones on the high end? It seems every country but the US already is being dominated by flip phones.