I too am a little skeptical about the importance of phosphate-free
antifreeze, but don't see any reason NOT to use it.  There are many
phosphate free antifreezes on the market besides the premium-priced
Autobahn from VW.  Prestone has one (silver bottle, not the familiar yellow
one) that sells for five or six bucks at Wal-Mart and other discount
outlets.  

Bill