FREQ CHANGE LATE; AFTER TKOF.

Narrative

MY FO WAS THE PF ON OUR FIRST LEG OF OUR 3 DAY TRIP. I HAD TAKEN THE RADIOS AND; UPON BEING CLRED FOR TKOF AND 'STAY WITH ME; TWR;' WE DEPARTED RWY 32L WITH THE CLRNC TO TURN R 040 DEGS; CLB TO 5000 FT. THIS PROC WAS COMPLIED WITH AND I PROBABLY MISSED THE FREQ CHANGE CALL; WHEN THE TWR CALLED US AND IMPERATIVELY TOLD US TO CHANGE FREQ TO DEP. I FLIPPED THE SWITCH ON OUR DUAL HEAD VHF AND DEP WAS IMMEDIATELY THERE AND GAVE US THE USUAL TURN TO 090 DEGS. I WAS MOVING FLAPS; CHANGING THRUST AND MOST OF ALL MAKING SURE OUR ENG ANTI-ICE ACTUALLY WAS ON. THE 'STAY WITH ME' STUCK IN MY MIND AND CONTRIBUTED TO MY LATE SWITCH OVER. TOTAL SITUATIONAL AWARENESS IS IMPERATIVE AT ALL TIMES AND WOULD HAVE SOLVED THIS INADVERTENT 'LOST COM.' CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR IS A RESERVE CAPT FLYING THE B-757 FOR A MAJOR UNITED STATES ACR. ORD IS HIS HOME BASE AND 'ORD CTLRS ARE THE BEST IN THE WORLD.' THE RPTR HAS FRETTED A LOT ABOUT HOW THIS MAY HAVE HAPPENED. 'STAY WITH ME' IS THE KEY. IT IS POSSIBLE THAT ORD TWR DID NOT CALL UNTIL LATE; BUT MAYBE THE RPTR JUST MISSED THE TWR'S CALL. RPTR WAS 'TOTALLY SITUATIONAL AWARE AT ALL TIMES' BUT CANNOT UNDERSTAND WHY THE FREQ CHANGE WAS NOT MADE. THERE WAS A LOT OF RADIO TFC AT THIS TIME.