James,
I wish I could tell you there was a better system out there but right now the best GSM modem I know of is limited to 19.2 KBPS and I dont think they have it set up in the UK yet. I have been following it for 3 years and the progress is worse then anemic. The one name i know of is novatel they currently have systems for the palm III and V and the site Handgear.com has some attachments to connect your palm to your phone ...I am just not to sure on UK availability.
Sean R. Spurrier
Consultant