WRONG FREQ ASSIGNMENT LEADS TO LOST COM.

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WHILE ON DSCNT TO GSH VOR; ZAU (132.05) HANDED OFF TO ZAU (120.35) WHO CLRED US TO 5000 FT. ON REACHING 5000 FT; COM BECAME ERRATIC THEN LOST. WE TRIED SEVERAL OTHER FREQ INCLUDING THE SBN APCH S FREQ 132.05. WHILE TRYING OTHER FREQ MONITORED 120.35. CONTACT WAS REESTABLISHED AND RECEIVED CLRNC TO 3000 FT. COM LOST AGAIN AND WAS UNABLE TO ACKNOWLEDGE RECEIPT. AT 3200 FT MSL WE BROKE OUT OF THE CLOUD DECK AND PROCEEDED TO EKM AND LANDED IN COMPLIANCE WITH FAR 91.185 PARAGRAPH B. CONTACT WITH TERRE HAUTE FSS WAS ESTABLISHED AND HE ADVISED THAT CTR WOULD LIKE A PHONE CALL. A CALL WAS PLACED APPROX XA55 AM AND CTR INDICATED THAT THEY WERE UNAWARE OF THE FACT WE WERE ON FREQ 120.35 AND THAT THEY USED THE SBN APCH FREQ (N SECTOR) 118.55 AT NIGHT. ALSO; THE CTLR WAS IN THE PROCESS OF BEING RELIEVED AT THE TIME. THERE WAS NO CONFLICT AND THE FLT WAS COMPLETED 'BY THE BOOK.' WE SUBSEQUENTLY LEARNED FROM THE ARPT MGR THAT HE HAD BEEN AROUSED BY A CALL FROM CTR AND ASKED TO CHK THE ARPT FOR THE ACFT. THE ACTIONS TAKEN BY CTR AFTER LOSS OF COM ARE TO BE COMMENDED. THE ISSUE OF INCORRECT FREQ SEEMS TO BE GETTING WORSE. IN THE DAY OR EVENING IT IS A MINOR MATTER. AT NIGHT; HOWEVER; IT CAN BE A REAL PROB. IN THIS CASE; HAD NOT VFR CONDITIONS BEEN ENCOUNTERED; WE WOULD HAVE HAD TO COMPLY WITH FAR 91.185 PARAGRAPH C. THIS WOULD HAVE BEEN COSTLY AND WOULD HAVE BEEN A TIE-UP FOR CTR. I HAVE NO SOLUTION EXCEPT TO RECOMMEND A LITTLE MORE PRECISION WHEN ISSUING FREQ CHANGES.