There's a similar system already in place in Japan, it's quite impressive. You can link a credit card to your phone and actually use it like a ticket at train gates, or buy stuff and pay the bills at convenience stores by scanning the phone. Adoption seems to be a bit slow though, probably because of the risk of linking a phone to a credit card, and sheer habit.

http://en.wikipedia.org/wiki/Osaifu-Keitai

Printing something on a label/piece of paper is still orders of magnitude cheaper than embedding a RFID tag...

Also, Gingerbread does not support writing from the device (i.e., your phone cannot act as its own RFID tag), I'm supposing the hardware support is there, though.