Hi there,
If it's 5 pin, i'd say it's an XLR-5 connector. This is the one used on the Airbus, not too sure about the 737. I bought a headset recently with the two individual plugs, designed for an earlier Boeing aircraft, and made the adapter to allow me to use it in the 'bus.
Sennheiser have a very good pdf file, which can be found at
http://www.sennheiser.com/sennheiser...ssignments.pdf, which contains all the different plug types and the connections in each of them.
Hope this helps
high-flyer