Oh my, this is happening sooner than I ever imagined -
Wired News: Debit, Credit or Cell Phone? Japan has long been phasing out the hassle of coins and bills with microchip-laden "smart cards," which let people make electronic payments for everything from lunch to the daily commute.
A series of phones going on sale this summer in Japan, for use on NTT DoCoMo's wireless network, are the world's first with an embedded computer chip that you can fill up with electronic cash.