I doubt very much that you will get this as a chip.

Especially for 20 miles, you'll almost certainly be looking at some sort of module.

At that kind of distance, you'll probably need a reasonable power - which probably means that you'll need some sort of licence.

Does it have to be a direct, point-to-point link, or could you use a service such as GSM or trunked radio?
http://en.wikipedia.org/wiki/Prof...bile_Radio
http://www.mobitex.org/
http://www.transcomm.uk.com/
http://en.wikipedia.org/wiki/TETRA

Look here for some ideas: http://www.rfsolutions.co.uk