I think that mobile payment is going to become increasingly common. I recently heard from Obopay, a mobile-to-mobile money transfer service, which has recently launched an iPhone-optimized website. It allows iPhone users to easily send money to any cell phone that can receive an SMS. It is specifically formatted for both the iPhone and the iPod Touch, viewable in landscape or portrait mode and optimized for both EDGE and 3G networks, for a fast and secure transfer.
To use Obopay, sign up at www.obopay.com. You can fund your Obopay account by linking your checking account or with a credit or debit card or with cash at any Green Dot location. Once you have an account, you can send money to any mobile phone on any network. When someone sends you money, you can either sign up for Obopay or just have it transferred directly to a bank account.
It costs $0.25 to send any amount of money up to $1,000. You can receive and withdraw money for free, regardless of the amount. Use of the iPhone-specific site is at no extra cost to users.