http://www.amazon.com/Introduction-Wireless-Systems-Bruce-Black/dp/0132447894
This is a text that deals with modulation and multiplexing techniques, theory of hardware required to accomplish those techniques, and the infrastructure needed to support large-scale wireless systems. Most of the examples given in this are based off of cell phone technology. I'm also a little biased to this, because the main author was my academic adviser in college (and I've taken classes with another contributing author).
The text is very easy to follow (but not didactic) and uses lots of diagrams!