On the Three network you must use 3G for data access, sometimes the APN profiles can cause problems and they need to be "refreshed" before the phone will correctly work on the Three network for 3G. The following information applies only to the San Francisco phone being used on the UK Three network.
1) Make a note of your existing APN settings (to restore if you experience any problems)
From the main Menu select "Settings", "Wireless & networks", "Mobile Networks" and then "Access Point Names".
For each of the APNs listed make a note of the details and then enter the following details (these details are for the UK Three network ONLY other networks will require different information which your provider should be able to supply). Once you have backed up your existing APNs remove them via the "Menu" button whilst reviewing the APN.
Modify the new APN details as follows (other options do not need to be changed)
Name: Three Network APN: three.co.uk APN type: Default
Then create a second APN (for MMS)
Name: Three Network MMS APN: three.co.uk MMSC: http://mms.um.three.co.uk:10021/mmsc MMS PROXY: mms.three.co.uk MMS PORT: 8799 APN type: mms
With the settings above your phone should reconnect and use 3G for data.