B737 FLT CREW LINES UP ON WRONG LOC APCH INTO LAX.

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INBOUND LAX VIA PDZ 4 ARR; APCHING ARNES; DSNDING THROUGH ABOUT 10500 FT FOR 10000 FT. FMS SET UP FOR RWY 25L; BUT WE HAD JUST RECEIVED CLRNC FOR THE PDZ TO RWY 24R WHEN THE FIRST FLT ATTENDANT RANG AND ENTERED TO ASK 'WHERE ACR X WAS' AT LAX. I WAS ANNOYED; THE FO TURNED TO ASSIST. AFTER A MIN; THE FLT ATTENDANT LEFT. I DINGED THE CABIN TO INDICATE 10000 FT STERILE COCKPIT; AND INITIATED A DSCNT AS WE ESTABLISHED OURSELVES ON THE LOC. AS THE FO TURNED BACK AROUND AND ASSESSED OUR POS; WE BOTH REALIZED WE WERE STILL WELL L OF THE RWY 24R LOC AND WERE; IN FACT; ON RWY 25L. SIMULTANEOUSLY; APCH ALSO NOTED WE WERE LINED UP ON RWY 25L AND ISSUED A HDG TO INTERCEPT RWY 24R. ALTHOUGH I NOW REMEMBER THE FO READING BACK RWY 24R; THE FLT ATTENDANT INTERRUPTING IMMEDIATELY THEREAFTER WAS SUCH THAT I DID NOT RERTE MENTALLY TO THE NEW RWY. THE FO; WHO WOULD NORMALLY HAVE NOTICED THAT I WAS ABOUT TO INTERCEPT THE LOC I HAD BRIEFED; RATHER THAN THE ONE WE WERE CLRED FOR; WAS TOTALLY DISTR. ARRS AT LAX ARE NEVER QUITE ROUTINE. NUMEROUS RWY CHANGES ARE THE NORM; AND I DON'T BELIEVE THIS ONE WOULD HAVE GOTTEN BY HAD IT NOT BEEN FOR THE UNTIMELY INTRUSION ON THE FLT DECK. MY COCKPIT WILL BE STERILE BY 12000 FT GOING INTO BUSY ARPTS WHERE THE ACTION STARTS WAY OUT.