I use the Belkin Tunecast Transmitter here for mine. When I asked Belkin why they were not for sale in the UK about a year ago, the guy said they are illegal as they transmit a signal which is effectively what a radio station does, thus you need a licence for it. He did say they were working with the broadcasting authority to overcome it so by the look of it they have.

I know of a few in the UK and they are about 20quid here.

Opinions on it: Signal is only as good as FM so gets crackly at times and it needs to sit close ish to the head unit which I cant do easily. For the price, it isnt much to lose if it doesnt work is the way to look at it I guess.

HTH a bit!