Hi,
The Messages app can do this.
The basic method is you have an AIM Account in Messages and display the Buddy List (Window menu).
You then add the Phone Number as it is were a Buddy with a leading +1 (As in +1234567890)
There are restrictions:-
1) the Computer has to set as if it is in the United States (System Preferences > Language and Text > Region)
2) The Phone has to be in the United States AND
3) Has to be on a carrier that supports AIM's SMS forwarding
The Leading +1 is in fact a country code but AIM have never rolled this out further than the Untied States.
Their site has a list of carriers on it somewhere.
10:35 PM Saturday; February 23, 2013
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