Surely it's just a case of contacting Virgin, asking for your PAC, and
passing it onto Three... when you are setting your new account up with
them??

1   Leave enough credit on sim card to call Virgin CS.
2   Buy Skypephone £39.99p (£49.99p with £10 credit included).
3   Register on My3, use up £10 credit on Internet Add-on, calls, texts etc.
4   Get PAC code from Virgin CS then call 3 CS on 333.
5   Three will credit £10 to your account after the number port has
completed.

Comments on Skypephone
Loudspeaker can be a bit jarring.
Quality of Skype calls was OK when I last used it.
Can be used as a Modem via Bluetooth or USB, (add-on permitting).

Not interested in Nokia 6120 ?
More expensive but includes HSDPA for faster internet access.

Alan