The other day I picked up a Vodafone 3G Data Card which gives me 384kbps* connectivity where ever** I am. Vodafone now supports PowerBooks and OS X and I must admit it works quite nicely. It acts like another modem device, so you just fire up Internet Connect and hit connect when you want to 3G it up. The installer also sets up a new network location which you need to switch to also. I assume this could be customised so you don't need to switch locations.

The deal is £52/month for unlimited usage*** which, even taking into account the fine print, is pretty good for anywhere-access.

* 64kbps up.

** where ever 3G coverage exists anyway, which is meant to be "60% of the UK population". Where 3G isn't available it seamlessly falls back to GPRS.

*** the fine print is actually "unlimited: * subject to fair use" where they define "fair use" as 1GB per month. Gotta wonder how they can claim "unlimited"...