I really believe cell phones will continue to play a much larger role in our daily financial lives, one example I experienced this week was the use of SMS to determine the balance of a prepaid debit card from Alltel. Having used a prepaid debit card in the past it is always a pain to get the latest balance details. You have to either make a call and quote all the numbers or you go online and register at yet another website.
With Alltel you are able to send a text from the your phone and get a balance text back within seconds. I think this is uber cool, I also believe that banks and their associated card vendors should offer something similar. You could potentially use this for credit cards and debit cards. The only real caveat being that you would have to define which cell phone numbers can request balance information. Some of the obvious security concerns could be overcome by establishing a secret PIN that you text, this could be setup during an online banking session.