Here is my free business idea of the day. It would be straightforward to take Lifehacker’s AIM BudgetBot and turn it into a more robust paid (or ad-supported) service for SMS-based budgeting and expense tracking. I hacked it myself into something I use, but it should be broader service.
So, why this approach? Well, because the trouble with expense tracking is a) that it needs to occur at point-of-expense, which implies mobile device, but b) you don’t want it tied to any particular mobile device (because what happens if you change?). The Budgetbot approach solves both problems.
So … one, two, three — go.