One more note about TDMA vs CDMA, you will get better service with the CDMA phones, as I said before, TDMA is obsolete and is slowly being phased out. If you live or travel through rural areas, CDMA is probably the best choice for you, as CDMA towers can transmit further than GSM towers and they generally have better rural coverage.
The great advantage of GSM phones is being able to store all your contacts on the SIM and swap phones without losing all that data. They are also compatible with GSM systems worldwide as long as they have at least one of the international bands (900/1800mhz, whereas GSM networks in the USA use 850/1900mhz). I like my CDMA coverage through Sprint, it works great in rural SW Georgia where I have family.