I'm impatient, so I called from work today (half expecting them to refuse / hit a wall)
Turns out I didn't need my 3 number. Called them up and gave them my postcode and my name, from there they pulled up my recent order and then asked me for my PAC code and the number I want to keep.
Once I'd given them the PAC they said the port would be complete on 12/10/11 aka tomorrow, and even told me my 3 phone number, until my port is complete. Not that it matters, but I thought it was nice of him to mention it.
When I got home my sim was waiting thanks to Royal Mail, so all I need to do on friday is pop it in the iPhone and boom!
Give them a call