I have just fitted a combined GPS/GSM roof aerial. It has two outputs, one for my sat-nav and another for mobile phone. It is a genuine part, was easy to fit although involved making a square hole in the roof :crazy: and looks great.
I have 6 brand new combined GPS/GSM aerials, internal mount/covert low profile, check link for specs....
http://www.mastercom.dk/gps154-6.htm
Anyone interested, then I'll take £40 each for them.