Was having no joy with downloaded settings
from Nokia but found these to work:

Homepage: http://wap.o2.co.uk
Proxies: Enable
Primary Proxy:
Port: 8080
Secondary Proxy: 8080

Bearer Settings
GPRS Access Point: payandgo.o2.co.uk
Authentication: normal
Login Type: automatic
User Name: payandgo
Password: password

Hope this helps, Will.

See More: GPRS settings for unlocked 7600's here: