DO328 EXPERIENCED POTENTIAL CONFLICTION DEPARTING PHL BECAUSE OF MISUNDERSTOOD HEADING CLRNC.

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THERE WAS A COMS BREAKDOWN BTWN ATC (TWR) AND THE FLT CREW PRIOR TO TKOF. ATC ISSUED TKOF CLRNC OF 270 DEG HDG; 5000 FT OFF RWY 27L. THE SAME CLRNC WAS READ BACK AND WE DEPARTED. UPON CLBOUT; TWR SWITCHED US TO DEP FREQ WITHOUT FURTHER INSTRUCTIONS. DEP CTL DID NOT RESPOND TO US (THEY WERE VERY BUSY) AND WE CONTINUED AFTER TKOF PROCS. AFTER A FEW MINS OF NO RESPONSE; WE CHKED THE FREQ AND SWITCHED TO THE APPROPRIATE ONE FOR OUR DIRECTION OF FLT. ATC TOLD US TO DISCONTINUE CLB AT 4100 FT AND TO LOOK FOR TFC AT OUR 1 O'CLOCK POS. WE HAD THE TFC IN SIGHT (VMC WX); ATC CONTINUED OUR CLB AND TURNED US SBOUND. WE RECEIVED NO CONFLICT RESOLUTION FROM TCASII -- THERE WAS ADEQUATE SEPARATION. ATC INFORMED US THAT TWR HAD EXPECTED US TO FLY A DIFFERENT DEP THAN WHAT WAS READ BACK AND PERFORMED. THERE ARE 2 FACTORS THAT CONTRIBUTED TO THIS SIT: 1) DURING HIGH VOLUME; HIGH WORKLOAD ENVIRONMENTS; THERE IS AN INCREASED CHANCE FOR COM BREAKDOWN AND A NEED FOR INCREASED VIGILANCE IN ATC READBACK ON BOTH ENDS OF THE COM. 2) BOTH PLTS ARE CAPTS AT THE AIRLINE. THE AIRLINE UTILIZES CAPTS FOR BOTH POS -- THIS CAN LEAD TO CONFUSION ON ROLES AND DUTIES (EG; WHO SETS THE DEP FREQ PRIOR TO DEP); TYPICALLY FO'S SET THE DEP FREQS DURING TAXI. THERE ARE OTHER NEGATIVE SAFETY ASPECTS OF USING CAPTS FOR BOTH SEATS -- IT SHOULD NOT BE ALLOWED. ANOTHER CONTRIBUTING FACTOR WAS THE 8 HR FLT TIME; AND 14 HR DUTY DAY THAT WAS SCHEDULED FOR THE CREW. THESE ARE REGULAR SCHEDULES -- THEY ALWAYS PUSH FLT CREWS TO THE MAX AND LEAD TO A DEGRADATION OF SAFETY. FLT AND DUTY TIME REGS ARE NOT REALISTIC; AND OFTEN DON'T TAKE INTO CONSIDERATION EARLY MORNING OR LATE NIGHT FLYING EFFECT ON FLT CREW'S PHYSIOLOGY. SUPPLEMENTAL INFO FROM ACN 601698: DEP ADVISED THAT TWR ASSIGNED 240 DEG HDG.