@Chris Gibson
No problems whatsoever with CID here either, and that includes international numbers as well. Sounds like an idiot who can't use their phone.
Funny thing is that with my old Nokia N80, it would regularly fail to match CID if I had more than one number for each contact. This resulted in having stupid entries like Fred Mobile, and Fred Home. The iPhone also displays who a number belongs to if you dial the number directly regardless of whether you dial the number as it is stored, or prefix it with 0044/+44 (in fact I just tried it with my home number and missed out the area code and it still found it), great for when you don't recognise a number on your bill. With the Nokia I had to actually call the number and hit end just before it connected before the phone would display the owner.