Please forgive me if this has been mentioned, but all I have read says otherwise...
If you see in your messages and NOT your call log or hot list, when you "add to address book" the number defaults to Mobile!
A little more specifically, I got a text from a number I didn't have, scrolled up to highlight it, hit the menu button, selected add to address book, and voila! It defaulted to mobile.
Hope this is helpful!! :-)
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