Phone number missing from the "receive at" section in Messages on iOS5

So upgraded my iPhone4 and the other halfs to iPhone4 to iOS5 yesterday evening.

However, on the OH's he phone number is missing from the "receive at" section in 'Settings >> Messages' doesn't give the ability to add it, only gives add for email addresses.

This means I have to remember on my phone when txting her to selct her email address instead of phone number otherwise it sends as a txt.

Any Ideas?