MLG LOST COM WHILE HOLDING IN POS ON THE RWY CAUSING AN ACFT ON APCH TO GAR.

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WE WERE TAXIING TO RWY 11R AT MSP INTL. WE USE COM 1 FOR ATC COM ON THE MLG. PRIOR TO TKOF WE PRESET THE DEP CTL FREQ AND TWR FREQ ON THE SAME COM UNIT AND THEN JUST TOGGLE FROM ONE TO THE OTHER. AS WE NEARED THE RWY I CONFIRMED THAT THE DEP CTL FREQ WAS SET ON THE L SIDE. THE TWR CLRED US INTO POS AND HOLD WHILE AN ACFT FINISHED HIS LNDG ROLL AND WE REFED THE NEXT ACFT ON A 3-4 MI FINAL. ONE OF THE LAST ITEMS ON OUR BEFORE TKOF MECHANICAL CHKLIST REQUIRES THE FO TO PUSH THE TKOF CONFIGN BUTTON TO CONFIRM A NORMAL CONFIGN MESSAGE PRIOR TO DEP. WE WERE IN POS ON THE RWY ABOUT 15-25 SECONDS AND HEARD NO TWR COMS TO ANYBODY. REALIZING THE FREQ WAS TOO QUIET; I CHKED THE FREQ ON THE #1 COM UNIT. THE TOGGLE HAD BEEN FLIPPED OVER TO THE DEP FREQ. I FLIPPED THE TOGGLE BACK; CALLED THE TWR AND WAS CLRED FOR TKOF. THE ACFT ON FINAL WAS FORCED TO EXECUTE A GAR. WE CONCLUDED THAT WHILE PRESSING THE TKOF CONFIGN BUTTON THE FO BUMPED THE COM #1 TOGGLE OVER TO THE DEP CTL SIDE. THE TKOF CONFIGN BUTTON AND THE COM 1 PANEL ARE SIDE-BY-SIDE ABOUT 2 INCHES APART.