Let’s be honest now.  Two-way User Profile Synchronisation in SharePoint 2010 isn’t actually two way. It’s one-way or the other.  Either stuff comes from the external store e.g AD OR the stuff come out of SharePoint into the external store. It don’t detect the latest change and sync accordingly.

You try it.  Set up a connection to AD.  Set the direction to be Export for say the mobile number. Then do a sync.  Your changes will go from SharePoint to AD only.  If you change something in AD it will get overwritten by the value in SharePoint.  If you change something in SharePoint it will update the AD correctly.

See.  Should be called One-Way or T’ther Synchronisation … not Two-Way.

Cheers

Dave Mc