Can i move my current mob no at a later date(Seen good k800i Deal)

[LordVader]

I seen a good deal over at simply3g for a k800i

http://www.simply3g.co.uk/handsets/three/sonyericssonk800i_clearance.htm

Its CLEARANCE but hopefully i dont get a dud

Question is my current orange contact dont run out till next month, will i be able to PAC my number over to three still at a later date?