Messaging via phone # on iPad?

Hi

I just got a new ipad and set up messaging. I enetered my apple ID and it pulled in my email, but not my phone #. I would like my texting to go through the phone #, not my email. I can't manualy add the # either.

I know this should work since the guy next to me has the same device and he texts via his phone #.

I checked my itunes account and my phone number is there.

Any ideas why it won't bring in the phone #, or let me add it?

Best

John