WHILE ON CLIMBOUT, THE STU PLT SWITCHED RADIOS TO THE DEST UNICOM FREQ. UNABLE TO CONTACT ANYONE ON THAT FREQ, THE DEPARTURE ARPT FREQ WAS RESELECTED. NO CONTACT WAS ESTABLISHED ON THIS FREQ SO THE STU PLT ATTEMPTED TO RTRN TO THE ARPT. THE HAZE WAS VERY THICK AND THE DEPARTURE ARPT WAS OVERFLOWN. AFTER ABOUT 30 MIN IT BECAME APPARENT THAT THE STU PLT WAS DISORIENTED. FOLLOWING PREVIOUS INSTRUCTIONS TO LAND PRIOR TO RUNNING OUT OF FUEL OR FLYING INTO NIGHT CONDITIONS, THE STU PLT STARTED LOOKING FOR A SUITABLE FIELD TO ACCOMPLISH THE OFF ARPT LANDING. REPORTEDLY THE ENG BEGAN TO RUN ROUGH DURING THIS SEARCH. AN APPROACH WITH AVAILABLE POWER WAS MADE TO A SOFT FIELD. UPON APPLICATION OF BRAKES, THE ACFT NOSED OVER. EXAMINATION OF THE ACFT REVEALED A VOICE ACTIVATED HEADSET AND AN UNLABELED SWITCH WHICH CONTROLLED COMMUNICATION OUTSIDE THE ACFT. THE NAVIGATION RADIO WAS NOT SET TO EITHER OF THE THREE VOR'S WITHIN RANGE. A WRITE-UP EARLIER IN THE DAY FOR THE ACFT STATED THAT THE COM RADIO WOULD NOT TRANSMIT.