Ive personally used the below:

http://www.eurocarparts.com/ecp/p/ca...1120&0&cc5_785

the interface is really easy to use, and it does the normal fancy things (sends youe text/emails with updates etc)

If its lost or stolen, the Road Angel team black out the screen and liase with the local police to recover it

If anybody wants to see the GUI in person, drop me a PM as we have a test account which used to be fitted to a test vehicle