imessage on phone number stopped working iPad and 10.8.2?!

Two days got back I got my iPhone 4 replaced with a new piece and is running on the same iOS 6. Since then however, while I can send and recive iMessages on my phone numbers, suddenly this has stopped working on my iPad and Mountain Lion 10.8.2.

I dont know if Apple has stopped giving this feature but i remember it working well untill a few days back

Any help?

Neerav