I can't select my phone number for iMessage (-sigh- Yeah, this problem again)

Let me explain the whole scenario:

My iMessage and FaceTime worked perfectly fine this morning.
I turned off my iMessage to check if I would be able to get messages from other iPhones.

My observation is that when an iPhone has their iMessage turned off and someone else who sends an imessage to that phone, their message would automatically turn to "text" messages instead of imessages. (Whoa, that sounds a bit confusing).

Anyway, I turned my iMessage back on and what do you know, I can't click my phone number because it's grey

I'm only able to select my emails. So for "send and recieve" it says "No address" (Because i didn't select anything, I'm waiting for my phone number to 'magically' get selected)

I have tried so many things and it's irritating.

My Facetime worked well, I would turn it off and back on and my number would get selected instantly. And I messed around with it, turning it off and back on to see if it'll automatically choose my number and it did. But I turned it off and on again and now It doesn't choose anything, it just says "Waiting for Activation"

But now after so many attempts of trying to turn it off and back on just to fix this iMessage crap, I can't even sign in to my apple id anymore. It says that I can't sign in and that I need to check my network connection. (I'm using wi-fi. And it's working perfectly fine; My network connection is fine)

So now, I'm really screwed. my iMessage and Facetime don't work anymore.

I'm really looking for a solution to this annoying problem.

By the way, it's an iPhone 4s and my carrier is T-Mobile.