Great idea. The bitcoins on phone can be changed to credit automatically. A phne that makes its own free credit.
In some places in Africa, cell phone minutes are actually used as a type of currency. Once someone figures out how to implement this idea (although I am skeptical until batteries can put out a lot more juice), OR trade bitcoins via SMS, I think we will have a MASSIVE market that opens up in Africa.
Good point about cell phone minutes.
I know there will be technical hurdles to overcome with regard to power efficiency, but I think it's inevitable that a device like this will exist, maybe *must* exist, when Bitcoin becomes ubiquitous.
We expect smartphones to be web-capable. The commodity phone of a few years from now will be web-capable and Bitcoin-capable. Things like calculators, personal organizers, watches, email, messaging, webapps have all migrated to cell phones. Bitcoin's turn is coming. The difference is you will be *paid* just to be connected, instead of the other way around. The same phone that might only earn enough
BTC per day to pay for one subway trip in NYC might put food on the table for a family in Nairobi.