I often use a little digital voice recorder to record the intercom during airtests. Saves me from having to write down the numbers during the 5 minute climb (although people have wondered about me talking to myself).
Made an adapter lead with a 3.5 mm plug on one end to connect to the voice recorder and a 6.3 mm plug on the other end to plug into a spare headset socket. In the lead I placed a 67 kOhm resistor and a 47 uF capacitor in series to adjust the output level of the intercom to the required input level for the mic input. Should work on other equipment that would normally use an external electret microphone (as most modern equipment does).
If anybody needs maplin part numbers let me know and I'll try to find a catalogue.
Cheers
Gerard