>>>There's a level of transaction which is below the small business but still larger than a few pence.
>
>Some phone providers already allow you to pay such fees by sending a txt to a designated phone number- e.g. it's already commonly available to pay for parking in some places. Smarter mobile payment options are due within a year.

The parking-via-SMS is commonplace in Belgrade since 2002 or 2003. There may be other services I'm not aware of, because I don't have a cell phone yet (and probably don't need it at all).