I have found that only the iPhone Signing Out with a removal of the Apple ID before hand and replacing on Starting Messages again followed by a restart of Messages on the Mac seems to solve this.
I would say the line about tapping the Apple ID may not be what everyone wants if they want to be seen sending from the iPhone Number, in Linc's listed method.
Please, if posting Logs, do not post any Log info after the line "Binary Images for iChat"
iMac 2.5Ghz 5i 2011 (Mountain Lion 10.8.2)
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb (Snow Leopard 10.6.8)
Mac OS X (10.6.8),
Couple of iPhones and an iPad
"Limit the Logs to the Bits above Binary Images." No, Seriously