what topic in communications? digital or analog? modulation? gsm? if there is a specific topic, probably we could give a more definite answer, or you could check on mathlab's demos, or the mathworks website www.mathworks.com for further information
for wireless digital systems, you have cdma blockset to simulate cdma systems, you could check matlab for help on the toolboxes or check on www.mathworks.com for added information and demos