unregistering a phone number from iMessage

So I got my iPhone 5, when I did I got it from another provider and backed up all the data from my iPhone 4. Because of this the iPhone 5 came with it's own number however I'm currently in the process of getting my number transferred to my new provider for my iPhone.

My iPhone 5 now though has 2 phone numbers it receives iMessages off, I want to delete the phone number my iPhone 5 came with but it won't let me (it's shaded out and won't let me un click it).

To make matters worse on my iTunes account I don't have any mobile numbers listed so I can't do it from there either.

So any ideas?, I don't want to use the new number I have been given and I don't want to get iMessages from random people once the number has been reassigned to someone else.

I have been able unclick on that number for my Macbook Pro, but on both my iPhone 4 and iPhone 5 I cannot delete that number from receiving iMessages.

 

Thanks.

Also my iPhone 4 is being sold, so I'm right just erasing it and then starting it up again (without my sim card in) will make it so nothing to me is related on that phone?

 

Cheers guys.