i'm with O2 at the moment and i was surprised that they are offering to keep your current number if you want to make the jump to the iPhone.
In the past, i've wanted to upgrade, but stay on the same network with the same number, and they wouldn't allow me to keep it ... always insisting on a complete new contract + number 😕
As for calling up for a PAC code ... i nearly lost it with T-Mobile in the past. The guy wouldn't give up the number and after asking what phone i was going to, just spent ages running my choice down. In the end i said "it my life mate, i didn't ask for your opinion so zip it, give me the number which you are oblidged to do, or forward me to the supervisor " ... soon shut up after that.
not decided about going for the iphone yet. i think i'll let the dust settle on the UK reviews and see what people think.