FLC SWITCHED TO TWR FREQ PREMATURELY.

Narrative

DURING TURN ON TO ILS RWY 22R ORD; I WAS ASKED TO REDUCE FROM 250 KTS TO 210 KTS; MAINTAIN 210 KTS AND GO TO APCH CTL ON 119.0. WE CHKED IN AND WERE CLRED FOR THE ILS RWY 22R; MAINTAIN 210 KTS; EXPECT 126.9 AT MARKER BUT MONITOR 119.0 FOR ANOTHER SPD REDUCTION. THE ACFT AHEAD WAS ON TCASII AT 4 MI RANGE. WE KEPT ENCOUNTERING RATHER SEVERE WAKE TURB AT TIMES SO I TRIED TO RIDE 1 DOT HIGH ON THE GS. I NOTED THE TCASII TARGET AHEAD CLOSING TO 3.5 THEN 3 MI AND THEN REALIZED WE WERE LISTENING TO ORD TWR. I ASKED THE FO IF WE HAD BEEN ADVISED TO SWITCH TO TWR; THEN REALIZED 119.0 HAD BEEN REPLACED BY 126.9 ON #1 COM HEAD. I TUNED 119.0 ON #2 HEAD; FLIPPED THE SELECT SWITCH TO #2 AND HEARD APCH CTL CALLING. (I HAD BEGUN SLOWING TO 170 KTS ON MY OWN DECISION TO MAINTAIN THE 3 MI ON THE TARGET AHEAD.) APCH CTL HAD BEEN CALLING FOR SEVERAL MI FOR US TO SLOW TO 170 KTS AS THE B757 AHEAD HAD SLOWED. WE WERE DIRECTED TO S-TURN TO R FOR SPACING; THEN GO TO TWR FREQ. TWR CLRED US TO LAND RWY 22R. THE LESSON LEARNED; AGAIN; WAS TO DOUBLE-CHK THE FREQ ENTERED BY 'THE OTHER GUY' EVEN IN SEEMINGLY GOOD WX. DURING OUR DEBRIEF; HE THOUGHT HE HEARD TO MONITOR TWR FOR THE SPD REDUCTION. THE EVENING 'BANK' AT ORD CAUSES NON-STOP RADIO ACTIVITY AND I'M NOT SURPRISED OF THE MISUNDERSTANDING/HEARING. MANY TIMES THERE IS NO OPPORTUNITY TO READ BACK DURING 'BANK' TIMES. A REAL SAFETY CONCERN!