you're are right, its a bummer no bluetooth on Golf's.
Anyway the media nav as you call it, is the RNS 510, which I retro fitted, a really great system.
There is a phone button, but this requires the purchase of the VW bluetooth module, some wiring and mucking around, but it is possible to retro fit, so it works with that phone button, however it wont be cheap, or covered by VWs warranty.
I have the Parrot Ck3100, which works perfectly with my RNS 510, never has any probs, and I believe some dealers will fit it for you.
theres a few threads on retro fitting bluetooth here:
http://vwnavi.com/forums/forumdisplay.php?f=51&order=descgood luck.