Actually, it IS possible.
You'll need to get into the engineering screen. Be careful in here as you can screw up your device if you're not careful.
Here's how to do it: Zibri's Blog: Hidden things are usually the best
1. Go to the engineering main screen
2. click mobile network enginnering screens
3. click Utilities
4. Click Session Manager
5. hit blackberry key and select UMA Options
6. Hit Blackberry key and New
7. Display name = Factory Provisions
8. Operator name = Orange
9. UMA Protocol = UMA V 1.0.3 (this is the default)
10.Uncheck use default UNC address
11. Enter UNC address 'unc.singlephone.orange.co.uk'
12. Provisioning UNC port '14001'
13. Uncheck box for use default provisioning SEGW Address
14. Enter SEGW address 'singlephone.orange.co.uk'
15. SEGW certificate select 'Equifax Secure Certificate Authority'
16. Hit blackberry key and select save