Won't receive message alerts

[+Ghost+]

After unlocking my Nokia 6800 from Cingular and using on a T-Mobile network, the phone can sent text messages, but wont receive them or voice mail alerts. I did a master reset and it still doesn't work. I sent a text message to itself and it worked, but when I send one from Nextel or leave a voice mail it won't work. Any ideas?

Thanks.

[+Ghost+]

I just checked. The correct service number is in the phone, so it aint that.