I used to have a CARK-91 when using my old Nokia 7160. The kit is amazing, and the audio mute feature worked perfectly. The Motorola kit I have now for my new T720 is complete trash. Where someone used to be able to hear me clearly on the highway with the nokia, I can now barely have a conversation on city streets.
A good place to order the kit from is
http://www.discountcell.com - I've ordered most of my phone accessories from them. As far as antennae go, find a good dual-band antenna. The aforementioned place should have them relatively cheap (~$30).
