I really hope not.
Drop your phone? Oops, can't buy groceries.
Accidentally leave your phone in the wash? Well, you didn't really need that prescription anyway.
Kid take apart your phone "to see how it works"? Oh, darn, the rent can wait.
Phone network down? Filling your car's gas tank is so overrated.
I'd rather keep my thin little (relatively) durable strips of plastic, you go ahead and use a smartphone.
http://www.google.com/wallet/
Either way.
Drop your wallet?
Oops. Can't buy groceries and your bank account is probably empty now and your prescription has already been filled anyway. Oh well.
Drop your phone, track it by GPS. I've had to do that twice.
Never seen a phone network down. But, I don't know anyone who carries cash on a regular basis, so if the phone network goes down.... then well they can't buy gas anyway.
You keep your real wallet that can be lost. I'll be ready to use my phone soon enough. Something I can track and if all else fails then quite literally destroy remotely. (HTC Sense is nice! lol)