FAILED TO COMPLY WITH CLRNC TO HOLD SHORT RWY 15L.

Narrative

VACATING THE ACTIVE RWY 25; SBA GND CTL CLRED US ON THE TXWY TO HOLD SHORT OF RWY 15R (AN INTERSECTING RWY USED FOR LIGHT ACFT). AT THIS POINT ON THE TXWY THE AFTER LNDG CHKLIST WAS COMPLETED AND I ADVISED THE CAPT THAT I WOULD BE OFF THE RADIO BRIEFING THE PAX AND CALLING OUR COMPANY WITH OUR ON/IN TIMES. THE CAPT VERIFIED TO ME THAT HE HAD THE RADIOS AND WOULD LISTEN TO GND CTL. DURING MY DEBRIEFING I NOTICED THE CAPT XMITTED SOMETHING TO GND CTL (WHICH TURNED OUT TO BE A REPLY OF 'ROGER' TO CROSS RWY 15R AND HOLD SHORT OF RWY 15L). THE CAPT MISUNDERSTOOD THIS AS CLRNC TO CROSS BOTH 15'S AND TAXI TO THE GATE. APCHING THE GATE AND BACK ON THE RADIOS; I HEARD GND CTL SCOLDING US BECAUSE WE HAD CROSSED AN ACTIVE RWY AND CAUSED A LIGHT ACFT TO ABORT. AS IT TURNS OUT; THE GND CTLR WAS CONTINUALLY TELLING US TO 'HOLD SHORT;' BUT WAS USING ANOTHER AIRLINE'S CALL SIGN; WHICH FLYS THE SAME TYPE OF ACFT AS OURS. WE BOTH SHOULD HAVE BEEN VIGILANT TO XING AN ACTIVE RWY AND LOOKING BOTH WAYS. I ALSO BELIEVE FULL LENGTH READBACKS IN CLRNCS WOULD HELP; BECAUSE THE RESPONSE 'ROGER' PROVED HERE TO BE NEAR DISASTROUS. THIS INCIDENT COULD ALSO HAVE BEEN AVOIDED IF OUR COMPANY DID NOT PRESSURE THE FLT CREWS TO SPEND SO MUCH TIME TALKING TO THE PAX; WHEN WE SHOULD BE OPERATING THE ACFT FIRST AND FOREMOST.