Payment via mobile phone is popular in South Korea but I haven't seen it really catch on in other parts of the world yet.
Mobile phone payments is starting to become popular in my country the Philippines. It's really a very convenient way to pay since we all carry our cellphones everywhere we go.
It was mentioned that you should use OboPay above... Unfortunately, Obopay canceled their prepaid or preloaded debit MasterCard service that was co-branded through Citi Bank last month. It might still work as a payment processor for you and they were supposed to take the lead in the mobile transfer of funds in the United States prior to the service changes with the recent preloaded card announcement and subsequent cancelations in March 2008. Best of luck.