Best answer by David AKU
If you are simply switching your SIM from an old phone to a new one, you need do nothing more.
If this is a new line, the SIM should have come pre-activated, and an email sent you to set up self serve.
If you are using a new SIM because the old one does not fit the new phone, you need to switch the SIM ID number in self serve. The SIM ID is on the SIM and the carrier card from which it is punched.