FLC OF ATX STARTED TKOF ROLL WITHOUT TKOF CLRNC DUE TO SIMILAR SOUNDING ACFT NUMBERS IN POS FOR TKOF AT THE SAME TIME ON 2 DIFFERENT INTERSECTING RWYS.

Narrative

IN POS ON RWY 1R AT INTXN F; AWAITING TKOF CLRNC. UNKNOWN TO US; ANOTHER GA ACFT WITH SIMILAR CALL SIGN (WE WERE XXX; HE WAS XXY) WAS IN POS ON 28R. TWR CLRED HIM FOR TKOF; BUT WE THOUGHT HE HAD CLRED US. I READ BACK THE TKOF CLRNC AS 'CLRED FOR TKOF ON THE R.' TWR SPOTTED THE ERROR AND CANCELED OUR CLRNC; AND WE STOPPED PRIOR TO 28R. I SHOULD HAVE SAID; '...ON RWY 1R;' NOT 'ON THE R;' BUT I SUSPECT MY READBACK AND HIS WERE SIMULTANEOUS; SO THE TWR PROBABLY HEARD NEITHER ONE OF US. SUPPLEMENTAL INFO FROM ACN 273604: THE CAPT ACKNOWLEDGED THE TKOF CLRNC ('CLRED FOR TKOF') WITH NO RESPONSE FROM TWR. I DIDN'T BELIEVE THE CLRNC WAS FOR US (MY GUT FEELING AND SUBCONSCIOUS INTERP OF WHAT I THOUGHT I HEARD); SO NO SOONER HAD WE BEGUN THE TKOF ROLL; I TOLD THE CAPT I DIDN'T BELIEVE THE CLRNC WAS FOR US AND ELECTED TO ABORT THE TKOF. THE CAPT ALSO PLACED HIS HAND ON TOP OF MINE AND PWR LEVERS TO CONFIRM THE ABORT. WHILE HOLDING SHORT OF 28L/R WE QUERIED THE CTLR AS TO WHETHER OR NOT TKOF CLRNC WAS FOR US. HE STATED THAT IT WAS NOT; BUT RATHER FOR AN ACFT WITH SIMILAR SOUNDING CALL SIGN. A TKOF CLRNC WAS GRANTED AND WE DEPARTED WITHOUT INCIDENT TO HAYWARD. OVER THE RADIO; THE CAPT APOLOGIZED FOR ANY CONFUSION AND THE CTLR SAID THERE WERE 'NO PROBS ON THIS END.' DESPITE THE FACT THAT THERE WERE NO PROBS; BOTH THE CAPT AND I LEARNED A VALUABLE LESSON. I ATTRIBUTE SOME OF THE PROB TO THE FACT THAT WE WERE ON OUR LAST LEG HOME AND PERHAPS LET OUR 'GUARD' DOWN SOMEWHAT. IN ADDITION; I WAS NOT PAYING AS CAREFUL ATTN TO THE RADIOS (AS I NORMALLY DO); SINCE I WAS REVIEWING OUR TKOF CLRNC AND FOCUSED ON FINAL ITEMS IN PREPARATION FOR TKOF.