Settings required to get internet working on the go with the Google Nexus One, which is running android version 2.1 are shown below.

3G Connection Setting

Settings / Wireless and Network / Mobile Networks / Access Point Names.
Hit the menu button and select new APN, and set the following:

• Name: O2 Mobile Web
• APN: mobile.o2.co.uk
• Proxy:
• Port:
• Username: o2web
• Password: password
• Server:
• MMSC:
• MMS proxy:
• MMS port:
• MCC: 234
• MNC: 10
• Authentication type:
• APN type:

Select 'back', and enable 'Data roaming'.

That's it for 3G settings.