Has anyone heard of or tried the adapter unit from Axxess Digital Interface?
The adapter looks promising, as it allows you to add Ipod functions to your OE radio, as well as add RCA inputs to it, or HD radio inputs (only 2 of the 3 though...still not bad)
I've found a lot of people using it on G6's and it works well so I bought one for my wife so she could use her MP3 player in her car (2005 G6 GT).
They claim it works in Mustangs 2005 and up.
After I install in her car (and it works) I might go ahead and buy the adapter harness and try in it my '08 and see if it does work...if so I can buy another unit and have my own (more interested in the HD radio myself, but having an Ipod connecter/interface would be nice)
Here is the website for the product http://www.axxessinterface.com/
For her G6 it cost around $135 (unit+GM harness+RCA) The place I ordered from was out of ipod adapters right now, but that would be another $29.99...everything would be the same price for the mustang (unless I went with HD radio which is a bit more)