B757 FLT CREW EXPERIENCES BOTH LNDG GEAR LIGHT BULBS IN THE INDICATOR BURN OUT; SO THEY DECLARED AN EMER; BECAUSE THEY WERE UNABLE TO DETERMINE IF THE GEAR WAS DOWN. THEY LANDED UNEVENTFULLY.

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NO INDICATION OF L MAIN GEAR. LACK OF ADDITIONAL EICAS MESSAGE INDICATED THAT THIS IS SIMPLY A BLOWN LIGHT BULB; ALTHOUGH A LITTLE UNLIKELY; DUE TO THE FACT THAT BOTH BULBS WOULD HAVE TO COINCIDENTALLY FAIL. UNABLE TO RESOLVE GEAR INDICATION BTWN ONSET OF PROB AND RWY; SO A MISSED APCH WAS PERFORMED. CONTACT WITH COMPANY MAINT WAS INITIATED; BUT RADIO RECEPTION WAS UNUSABLE DUE TO PROB WITH THE GND EQUIP. SEVERAL ATTEMPTS WERE MADE TO RE-ESTABLISH CONTACT WITH COMPANY MAINT; TO NO AVAIL. WHILE BEING VECTORED BY SAN ANTONIO APCH; I NOTICED THAT THE ANTENNA RECEPTION ON MY CELL PHONE SUDDENLY PEAKED. WE ASKED APCH IF WE MIGHT ENTER A SERIES OF 360 DEG TURNS (OVER THE CELL PHONE GND ANTENNA); WHICH WAS APPROVED. CONTACT WAS MADE WITH MAINT VIA CELL PHONE; AND THEY ADVISED A TWR FLY-BY. ENSUING FLY-BY INDICATED THAT BOTH MAIN GEAR APPEARED TO BE IN THE SAME POS (STILL BEFORE DAYLIGHT; AND DIFFICULT TO SEE); SO AN EMER WAS DECLARED; EQUIP REQUESTED; FOLLOWED BY UNEVENTFUL LNDG. TRUCKS FOLLOWED THE ACFT INTO THE RAMP; WHERE THE MAIN GEAR WAS PINNED. MAINT CHANGED BOTH BULBS IN THE GEAR INDICATOR; AND BOTH BULBS INDICATED DOWN AND LOCKED.