Note to Londoners: your telephone dialling code is not 0207 or 0208.

It's 020, followed by a 7 or an 8, and then your old number. That may sound like I am splitting hairs, but there is a real distinction:

If your old number was (0171) 654 3210, then your new one is (020) 7654 3210, not (0207) 654 3210. Got it? If you are calling from within London, you don't need the 020 bit, but you do need the 7.