MDT CORP ACFT HAS WRONG FREQ AND IS OUT OF CONTACT WITH ATC.

Narrative

WE WERE SWITCHED FROM NY CTR TO BOS CTR OVER DPK VOR (134.0). WE CHKED IN ON BOS FREQ FO (PNF) THEN STARTED MAKING A FLT PHONE CALL AND I MAINTAINED ATC COMS. I RECEIVED AND ACKNOWLEDGED A CLRNC FROM 16000 TO 15000 FROM CTR AFTER LEVELING AT 15000 THE FO CONCLUDED HIS FLT PHONE CALL (APPROX 2 MIN TOTAL TIME OFF FREQ). I REMARKED THAT IT WAS ODD WE WERE XING MAD AT 15000 AND 350 KIAS INSTEAD OF THE NORMAL 11000 AND 250 KIAS. THEN NY CTR CALLED US AND TOLD US TO RETURN TO BOS ON 134.0. WE EXPRESSED AMAZEMENT TO ONE ANOTHER BECAUSE WE THOUGHT WE WERE ON THAT FREQ. WE SWITCHED TO 134.0 BOS TOLD US WE HAD CHKED IN OVER DPK AND SUBSEQUENTLY HAD LEFT THE FREQ. THEY SAID WE HAD TOTALLY DISRUPTED THEIR AIRSPACE. NEITHER ONE OF US COULD RECALL SWITCHING UHF FREQS. THIS OCCURRENCE HAPPENED AT THE END OF A 12 HR DAY. WE FLEW FROM MADRID TO GANDER TO PHL TO BDL. WE FLY THE PHL-BDL RTE VERY FREQUENTLY. WE WERE VERY TIRED AND OF COURSE COMPLACENT BECAUSE WE FEEL WE KNOW THE RTE SO WELL. I DON'T THINK WE ACTUALLY VIOLATED ANY FAR'S; BUT OF COURSE I DON'T KNOW EXACTLY WHAT HAPPENED TO ALL OF BOS CTR'S TFC WE DISPLACED; AND WE STILL DON'T KNOW HOW WE MANAGED TO CHANGE THE UHF FREQS.