Samsung Galaxy S III (T-Mobile)

Does anyone have any information on how the MirrorLink on this phone works? I'm looking into buying this phone with a Sony XAV 601BT (in-car MirrorLink system). I'd like to get some information how that connection actually happens. I understand that I will have to connect it to a MHL cable, but I don't know anything beyond that.

How does it interface? Is it controlled by software on the phone? Is there something that needs to be downloaded into the phone? Is it all controlled remotely through the in-dash unit? Any information that anyone has on MirrorLink specifically with the Galaxy S3 is appreciated.

Thanks.