B737-700 CAPT INADVERTENTLY TAXIED ACROSS RWY DURING TAXI IN DUE TO BELIEVING THAT IT WAS AN INACTIVE RWY.

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NORMAL DAY/VFR (VISUAL) APCH AND LNDG TO RWY 3 IN ABQ. UPON ROLLOUT AT APPROX 60 KTS; TWR INSTRUCTED US TO 'EXIT AT TXWY C AND CONTACT GND.' MY FO DID NOT REPLY TO THE FREQ CHANGE AND I THEN CALLED FOR 'FLAPS UP CLEAN-UP' AS WE EXITED THE RWY ASSUMING THAT HE HAD SWITCHED TO GND CTL FREQ. AS WE ROLLED THROUGH RWY 12/30 (NOT LISTED AS AN ACTIVE RWY ON ATIS) MY FO ASKED TO SWITCH TO GND AND TWR ADVISED HIM TO 'SWITCH TO GND ON 121.9; PLEASE.' GND ADVISED US TO 'HOLD SHORT OF RWY 8 ON TXWY C' AND ASKED US IF WE REALIZED THAT WE HAD CROSSED RWY 12/30. I TOLD GND 'YES; AND THE ONLY INSTRUCTIONS WE RECEIVED WERE TO EXIT AT TXWY C AND CONTACT GND.' I ASKED GND IF I SHOULD CONTACT HIM ON THE TELEPHONE AND HE STATED TO BE 'MORE CAREFUL' AND HAVE A NICE DAY. I HAD KNOWINGLY CROSSED RWY 12/30 AFTER VISUALLY CHKING THE RWY 12 AND THE APCH TO RWY 12 FOR ANY ACFT. BEFORE MOVING; I SHOULD HAVE ASKED TWR TO 'SAY AGAIN FOR COMPANY NUMBER' AND I SHOULD HAVE TOLD MY FO TO SWITCH TO GND WHEN I HEARD THE INSTRUCTIONS; ALTHOUGH IT IS A SHORT DISTANCE ON TXWY C BTWN RWYS 3 AND 30/12. TWR SHOULD HAVE INSISTED ON A READBACK TO HOLD SHORT OF AN INACTIVE RWY.