i have been in the same boat and i went against it.
here are some reasons:
1 - wide footprint, not comfortable in pocket (based on tech specs)
2 - that pretty numpad won't be pretty long (based on user reviews)
3 - if any water (even sweat?) gets on keypad, it will die (MUTLIPLE user reviews)
4 - Razr V3x is due to come out VERY SOON. If you get a razr now, poop on you!
i got a 1000 minute t-mobile plan and that got me a free Motorola V330 and I must say its a very nice phone. However, a week later I got on ebay and gotmyself a Sony Ericsson V800 and its been great so far.
As for service, I'd stick with what you know. Not only do you know what to expect from the service, you will also save about $10/month on your bill vs Cingular ($120/year is good money imo you can be saving). I am sure the Cingular service is just fine, its that just well, why fix it if it ain't broke.
Also, if you do get an Asian/European phone like i did, chances are it won't work with Cingular as well because they use a frequency those phones don't support (Tmobile doesn't use it, so the Asia/Euro phones work just great).
I highly suggest you take a look at www.gsmarena.com
for a day or 2 and see what you like.
if you don't need bluetooth, I'd highly suggest the Asus J105