A B737-300 pilot reports an inoperative flight station headset forcing the flight crew to use hand mikes and earphones. The MEL governing deferred operations with an inoperative headset is confusing and inaccurate.

Narrative

Areas of concern: 1. MEL 23-14 covers headsets not aircraft headset jack malfunctions (suspected). 2. Aircraft had been misdiagnosed on previous day for Ground Crew comm jack inoperative. 3. Duty Control indicated a history of similar problems dating to late April 2009; yet aircraft was not properly troubleshot nor fixed. 4. MEL 23-14 language regarding inoperative boom mike/CVR nexus is confusing and; I believe; inaccurate. 5. MEL 23-14 language regarding TSO headsets vs personal headsets needs to be better clarified. Is a privately owned TSO headset covered? 6. Relief in this situation (a perfectly good Company-issued headset rendered inoperative because of an aircraft malfunction); if valid; is a potential safety concern vis-a-vis our new requirements to be very much 'hands on.' Difficult and cumbersome while using hand mike and listening to a poor-quality overhead speaker. 7. Check Airman I spoke with indicated other aircraft have similar problems and have not been fixed. 8. Despite my willingness to continue after assurance aircraft would be taken out of service upon reaching next maintenance Base; the aircraft continued in service for the day. Operating with hand mike and speaker is fatiguing and distracting; and combined with any additional abnormality (weather; other maintenance issues; long crew duty day; etc); compromises safety.