I have for sale a used 3 Mobile Broadband Dongle. It has been unlocked, and has been tested as working on XP and 2000. I have tried but failed to get it working on Windows 7 (something to do with firmware) so will assume that it won't work yet on Vista either.
Works great with XP netbooks, and obviously you can put any sim into it from your favourite network.
Comes minus the cap, but it excellent cosmetic condition.
Now confirmed working on Windows 7
included in price - 1st class.