I asked essentially the same question back in April, and did a poll too

do a search on cell phone service or Nextel or the like and you'll find it. The poll results were quite interesting though I for proper design it should have been two questions, 1) Who is your current cellular provider, and 2) Who would you never use again?
Also, try
letstalk.com and
inphonic.com for some good deals.
HTH