FYI, the monster cable option is okay. I use it currently. MY opinion on it is this though, if you want to make calls without holding the phone, its not what you want. If you like hearing the intermittent now and then transmissions over GSM frequency "Nit.Nit.Nit.Nit.Nit" every now and then, go for it. I have it, wont keep it, waiting for Alpine to release a similar product for iPhone. See link
http://www.alpine-usa.com/US-en/prod...model=iDA-X100
I tested one of these out at best buy with my iPhone worked great! Wasn't able to try the bluetooth pairing because well of course it was a demo floor model but they let me plug the jack into my phone and it was phenomenal.
Don't waste money on FM Transmitters, at least look into direct contact solutions, ie Cassette loading, or aux-in jacks, most decks these days have at least an aux in, or a port to plug an aux-in on the back, or a wiring option that you can purchase to install yourself or at the store. And for cheap.
The Monster Transmitter does nice, but the biggest down fall of any over the fm transmission is anyone else on that frequency can jump in with their tunes or fuzz you out. Now tell me your driving down the highway listening to your best tracks when all of a sudden some Birtney Spears loving dude with a mullet comes up behind you, and all you get to hear is "opps I did it again" it is not the most pleasant thing. No transmitters ppl, no way. If you are doing it for a temp quick fix, I say yes, but dont fork out the big bucks for it.