CLRNC LNDG NOT RECEIVED. UNAUTH LNDG. FREQ CHANGE MISSED.

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WE LANDED ON RWY 28R IN SFO WITHOUT ACKNOWLEDGING OUR CLRNC TO LAND. THE REASON WE DID NOT ACKNOWLEDGE IS BECAUSE WE NEVER SWITCHED FREQ TO THE TWR CTLR. WE WERE DISTRACTED BY AN UNUSUAL EVENT. AIR FORCE 1 WAS BEHIND; FOLLOWING US. WE WERE DISTRACTED THAT WE DID NOT CHANGE TO TWR FREQ; IN FACT WE THINK THE BAY CTLR WAS DISTRACTED SO HE FAILED TO GIVE US A FREQ CHANGE. AFTER LNDG WE REALIZED OUR MISTAKE BECAUSE WE DID NOT HEAR A 'HOLD SHORT' OR 'CROSS' CLRNC. WE WERE HOLDING SHORT OF RWY 28L AND WONDERED WHY WE COULD NOT HEAR THE TWR. IT WAS THEN THAT I REALIZED THAT WE WERE STILL ON BAY APCH FREQ 120.35. A CONTRIBUTING FACTOR IS THAT THE NORMAL FINAL APCH FREQ IS 135.65. TWR IS 120.50. I THINK! MADE A 'TWR CONNECTION' WITH THE SIMILAR FREQ. (120.35 VS 120.50). SUPPLEMENTAL INFO FROM ACN 296818: FROM ABOUT 20 NM OUT WE HAD WHAT SEEMED LIKE A LOT OF TFC TO LOOK FOR. AROUND 4 NM FINAL CAPT ASKED ME; ' ARE WE CLRED TO LAND?' I SAID; 'I DIDN'T HEAR ANYTHING.' HE SAID; 'WE MUST BE; THE RWYS IS CLR.' I SAID; 'YEA; I DON'T SEE ANYONE.' WE LANDED; TOOK THE HIGHSPD AND STOPPED BTWN RWY 28L AND RWY 28R. IT WAS AT THIS POINT THAT WE BOTH SAW 120.35 IN THE RADIO AND NOT 120.50. WE THEN CALLED TWR ON 120.50; THEY CLRED US TO CROSS THE RWY 28L. TWR ASKED IS THIS THE FIRST YOU HAVE HEARD FROM US. WE SAID;' YES.' AS IT WAS. CALLED GND AND TOLD THAT WE WERE SORRY. THEY 'SAID NOT TO WORRY; NO PROB. AT THE GATE THE CAPT CALLED THE TWR ON THE PHONE AND THEY SAID THEY UNDERSTOOD WHAT HAPPENED. WHEN I'M THE PNF I ALWAYS MAKE THE STATEMENT 'CLRED TO LAND' AT THE END OF THE 'LNDG' CHKLIST EVEN THOUGH IT WAS NOT ON THERE. THIS BACKS ME UP THAT THE PF IS CLRED TO LAND. BUT; WHEN I'M FLYING I DON'T ALWAYS HEAR THE CLRNC; CAUSE I'M FLYING. I DON'T HAVE A CHK TO BACK UP THE CLRNC OTHER THAN THE PNF.