PDAcoupler

Here's the idea: use multimedia-capable PDAs (such as my iPaq 3850) to send and receive digital data over plain telephone lines, using them as acoustic couplers. A software on the handheld would generate the sounds on the speaker and receive sounds over the microphone. You would just have to put the PDA near the phone.

You could use such a device for instance to send drawings or pictures while talking to someone over a normal telephone (provided that the other party has a similar device receiving data). You could also use the software as a voice encryption mechanism (just speak into the microphone and have the device encrypt your voice and retransmit it over the line).

Razvan