I activated my new SIM card, and this was accepted. But still nothing. When I try to phone, I get the message that the phone is not registered on the network.
Did you just activate it, or has it already been 30 min - a few hours? Have you reset the phone? Power cycled it by turning your phone off, taking the SIM card out, putting it back in a minute later and turning the phone back on?
If you haven't waited a few hours, you might want to try being patient as the porting might still be in progress. If time passes and it still gives you an error like that, you may want to contact a Moderator.