Yes. I have had AT&T cell phone service for a long time, and I have been paying online for years. Just go to their wireless website, and click "Log in | Sign up now" to sign up. For fear of being reported for spam, I will just tell you to Google their website.
Once you sign up, they will send you an e-mail each month when your statement is ready. I think you will have to choose the option not to receive a paper bill of you want to go paperless, but getting all of that set up is fairly straightforward.