WHILE FO COORDS WITH COMPANY; CAPT ACKNOWLEDGES CLB CLRNC MEANT FOR COMPANY WITH SIMILAR CALL SIGN. ZAU CTLR CHALLENGES CLB; RETURNING THE FLT TO ORIGINAL ASSIGNED ALT.

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WE HAD ENTERED HOLDING OVER JVL VORTAC AT FL280; DEST (MKE). WX WAS BELOW LNDG MINIMUMS. CAPT WAS PF. I WAS OFF CTR FREQ TO ADVISE PAX OF DELAY AND TO CONFER WITH OUR DISPATCHER ABOUT ALTERNATES AND CURRENT ALTERNATE WX. I HEARD PIC ACKNOWLEDGE CLRNC TO FL310 AND START CLB. I RETURNED TO FREQ AND PIC ADVISED ME OF OUR CLRNC TO FL310. CLBING THROUGH FL295; CTR QUERIED US AS TO OUR ALT. I ADVISED CLBING THROUGH FL295 TO OUR CLRED ALT OF FL310. CTR SAID THAT CLRNC WAS FOR A COMPANY FLT. HE TOLD US TO MAINTAIN FL280 AND FOR COMPANY TO CLB TO FL310. CTR FREQ WAS VERY CONGESTED DUE TO OUR DEVS. WX CELLS WERE BUILDING ALL AROUND US. WE IMMEDIATELY RETURNED TO FL280. WE BELIEVE NO LOSS OF SEPARATION OCCURRED. WE DECIDED TO DIVERT TO OUR ALTERNATE ARPT AND LANDED WITHOUT INCIDENT. FACTORS CONTRIBUTING INCLUDE THE INABILITY OF USING BOTH PLTS CONCERNING AN ALT CLRNC WHEN ONE PLT LEAVES FREQ; THE FREQ CONGESTION POSSIBLY BLOCKING A CRITICAL CLRNC READBACK; AND THE ONGOING PROB OF SIMILAR SOUNDING CALL SIGNS.