1) Connect Laptop1 sound-card audio-in and audio-out to appropriate small speaker(s)/mic (1) ; add your favourite *nix; 'cat <pre-made signal file> > /dev/dsp' 2) Same setup Laptop2 is listening for xxx signal level on mic input - writes a 1 to a file in RAM tempfile when above predefined level, then a 0 when below - insert appropriate programming magic to monitor tempfile and interface to something useable... 3) Profit!!! (Or IP-over-Audio) Elroy. (1) Would the laptop built-in ones be sensitive/powerful enough?!? NOTES: 1) Maybe different frequencies for each units send/receive so Duplex can be achieved?!? 2) Sorry Michael! Michael Fincham wrote:

How about a couple of old analog modems with 9v batteries to simulate being connected to a line, along with a little audio amplifier / receiver? I see duplex being a problem in that situation, but it's a start...

As an aside, we had briefly discussed the possibility of establishing an RFC 1149 IPoAC link for VPN back to the office for our man on the ground at NZNOG but the link quality was deemed unsuitable.