You've got a computer (your phone), communications, mobility, authentication, and a tie to a financial clearing entity (the telco provider).
Mobile payments is a huge and growing area. Especially outside the US, where banking/financial infrastructure is limited but mobile phones have skyrocketed due to bypassing the last-mile problem (throw up a tower and you've got coverage in a village or small town).
Even within the US there's a lot of work toward enabling mobile payments (and related financial services). Some of it tied to increasing spending propensity (people spend more when they don't deal in cash), some with social networking, some with data mining/tracking (your cell phone emits a wealth of data on you).