Is it possible to find out someone's number through their email/text?

I know this may sound stupid, but just want to be sure.
Not long ago, I gave my friend my mobile number. He texted me, but instead of showing his number it shows his email address. When I reply back, it goes to him like a normal text.
I can only contact him through the phone, like he hasn't got Facebook or anything. I'm out of credit till end of this month. I have free calls, so i can only call up. We have no mutual friends either, so can't get it off them.

Either way, is it possible to find out his number somehow through his email address that is obviously connected to his text messaging?

Btw, its an hotmail email address and its from an iphone.
(Sorry if Q's in wrong category)

You can only find it if he puts it there

Highlight their user name, press "F3". Hold "Shift" and press "end". Wait about 30 seconds and then hold "alt" while you type in their email address. Then press "enter'