Interesting article on The Register today. It looks like the UK, despite our growing dependence on mobile devices (see The Times today for more information), isn't using them for payments. Only 14% of Brits are using mobile payments on a regular basis.
I suspect that the issue here is that the maturity and penetration of our existing cards and cash infrastructure is making it difficult for mobile to take hold.... But the take-up elsewhere around the world clearly shows the potential is there.