The results from the Brummie jury...
For the record (now that everyone has forgotten about this story!) I did some quick back-of-the-fag-packet test on the train between London and Birmingham using speedtest.net. And this is what you get:
3G (stationary in Coventry) using T-Mobile and a phone with a USB cable:
ping: 207
download: 0.15 Mb/s
upload: 0.05 Mb/s
3G (100mph-ish) - two tests:
ping: 223 / 400
download: 0.2 / 0.05 Mb/s
upload: 0.05 / 0.05 Mb/s
Onboard WiFi (100mph-ish) - two tests:
ping: 241 / 185
download: 0.91 / 0.85 Mb/s
upload: 0.31 / 0.26
So, pretty good. AND, maintaining a 3G connection for the 45 minutes in the countryside between the M25 and Coventry was a chore. But in cities 3G is fine, good enough to maintain a VNC connection. And you can't watch BBC iPlayer because it thinks you're in Germany (love those German adverts).
75p per 10 minutes? It's not outrageous, but if you can use 3G then you might as well at those times it's possible.