OnlineA group of German students at FHTE have been working on a comprehensive history of telecommunications. I find their timeline a particularly useful way to navigate through their site.
The Norwegian Telecom Museum's website is worth a visit for obtaining further background material.
Another resource is the Media History Project - good for lots of useful links elsewhere on the world wide web.
Don't forget the Science Museum websites.
You may also want to take a look at Bramblyte School's questionnaires. These were created by students for visitors to the Telecommunications Gallery.
Alternatively, you might want to view a year 5 student's project researched at the Telecommunications Gallery.
Grolier's Multimedia Encyclopedia contains a series of concise articles on telecommunications. Well worth a read.
Compton's Encyclopedia has a very thorough article on radio.
Sneaky teachers will have already realised that the individual letters from the code gallery pages can be saved onto a disk to make up your own messages. To make this even easier, the Semaphore and Flag Alphabet symbols have been collected together in zip files to download quickly. The pictures are in windows metafile format, so they can be resized without any loss of quality.