Credit card in phone? Why not phone in credit card?

I'm at the Digital Money forum in central London today, braving the assorted anarchists & other protesters messing up my city.

As usual at this type of event, there's quite a lot of breathless hype around mobile banking, payments, NFC and so forth. Some of the usual commentary about your phone absorbing your wallet.

By coincidence, my eye also fell on this announcement today. A 3mm-deep cellular module for M2M applications. It made me wonder whether it could easy and cheap to create a wireless-connected credit card. Add an antenna, a slim battery - and maybe even a small screen or touchpad. Maybe even an NFC chip if you really want. I'd guess you could create a 4mm or 5mm deep credit card that's fully mobile-enabled.

Why bother going to all the hassle and cost of integrating with a phone, and dealing with the current brittle distribution and value chain for handset distribution?

If you want mobile payments, isn't it easier to mobilise what works already (credit/debit card) rather than try to shoehorn financial transactions into an existing device and value chain?