I've come across this information before - now that I've encountered it again, I wanted to take the opportunity to post it here (which I should have done the last time). Or perhaps this has already been posted - I don't know. This article states that AT&T and T-Mobile use a type of technology that can expose a customer to much more radiation - and more harmful radiation - than if the customer used Sprint or Verizon:
http://www.prlog.org/12106833-your-cell-phone-company-may-affect-your-risk-of-brain-cancer.html