Sindy, there is not any reprogramming necessary. To switch phones just move your SIM. All your information is on your SIM card. The phone needs to be unlocked (so that it is not restricted to a particular SIM, or a particular carrier's network), and make sure the phone uses the same network standard (GSM for tmobile and cingular, CDMA for Verizon, etc.).

The phonescoop site that Mike gave you is a great way to look up what phones would be compatible with your network. You could also go to the retail store for your carrier and check out what phones they offer.

 

After much personal debate, I opted to buy a phone from my carrier after all.
I selected a smart phone with all the bells and whistles. I'll be comuting to work many hours a day here soon. I could multi-task during the ride to at least try to make sitting in a van-pool vehicle more productive.
I selected a Cingular 8125 PDA Phone.
Thanks for ya'lls input!

 

Darn, I wasn't quick enough! I bought a Sony Ericksson S710a almost a year ago and paid $200 for it after the rebate. But I have to tell you, it's the best sounding phone I've ever owned. The MP3 player and camera work well also. It's internet and bluetooth capable. I use it for all my long distance calling and never have a problem. It works well all over the country. Of course, that may just be Cingular's network. I'll pay the price and buy another Sony Ericksson any day!

 

I believe I have a month to try the equipment.