CLASS D AIRSPACE INCURSION AND RWY INCURSION; LNDG WITHOUT CLRNC; BY A PA24 PVT PLT AT TUP; MS.

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WE WERE TRYING TO LAND AT CORINTH; MS. WE WERE VFR ON TOP; 5500 FT MSL BUT HAD JUST PASSED TUPELO; MS; AND IT WAS STILL VFR. WE DECIDED TO GO A LITTLE WAYS AND SEE IF POSSIBLE WX WOULD IMPROVE SO WE COULD LAND AT CORINTH. IT DIDN'T SO WE TURNED AROUND FOR TUPELO AND ADVISED ZMP WHO WE WERE TALKING TO; VFR FLT FOLLOWING. WE WENT SLIGHTLY S OF TUPELO; SQUAWKED 1200 AND DSNDED VFR; TURNED N TOWARD TUPELO. I ASKED MY PAX TO GIVE ME TUPELO TWR FREQ AND HE SAID 118.75. I GLANCED AT IT AND CONCURRED. TRIED CALLING SEVERAL TIMES BUT NO RESPONSE. I THEN LOOKED AT MY FLT GUIDE AGAIN AND NOTICED A 'CTAF' OF 123.05. I ASSUMED THAT MEANT IF TWR WAS NOT WORKING THEN 123.05 WAS THE CTAF. I CHANGED TO IT AND BROADCASTED MY POS THROUGHOUT THE PATTERN AND LANDED. AFTER LNDG I LEARNED THAT TWR FREQ WAS 118.775 NOT 118.75 AND 123.05 WAS UNICOM. I CALLED TWR ON THE PHONE; APOLOGIZED AND TOLD THEM I WOULD CHK MY RADIOS. UPON RETURNING TO THE PLANE MY TOP RADIO WAS ON 118.75 AND BOTTOM WAS ON 123.05. THE PROB AROSE BECAUSE I CHANGED MY DEST ARPT AND DIDN'T HAVE TIME WHILE FLYING THE AIRPLANE IN MARGINAL VFR TO FULLY REVIEW THE FLT GUIDE. I'VE NEVER SEEN AN ARPT WITH A 'CTAF' THAT WASN'T ALSO THE TWR FREQ AND I STILL DON'T UNDERSTAND THAT BUT I WILL SOON.