How to move iMessage account to different mobile phone number

Question

Hello
I am going to change mobile phone number and I would like to know how
1) move iMessage/faceTime to this new phone number
2) how to transfer the "history" (old messages) from my old phone number to the new one
thx

Answer 1

Hello, matteos72. 
Thank you for visiting Apple Support Communities.
Make sure that your new number is updated in Settings > Phone > My Number.  Once this done, follow the steps in the quoted section below.  Next, sign back into iMessage and FaceTime.  The history will not be modified as no data is deleted. 
Unlink a phone number
To remove a phone number from an Apple ID, sign out of FaceTime and Messages on your iPhone:
Settings > Messages > Send & Receive. Tap your Apple ID, then tap Sign Out.
Settings > FaceTime. Tap your Apple ID, then tap Sign Out.
This should remove your phone number from other devices using the same Apple ID with FaceTime and Messages. If the phone number is still available on other devices after you sign out of FaceTime and iMessage on the iPhone, you may need to sign out of iMessage and FaceTime on all your devices, then sign in to FaceTime and Messages again on devices you want to use.
Note: If you no longer have access to the iPhone that is using the number you want to remove, reset your Apple ID password.
iOS and OS X: Link your phone number and Apple ID for use with FaceTime and iMessage
http://support.apple.com/kb/HT5538
Cheers,
Jason H.