RWY 27 INCURSION DURING A CALL SIGN MIX UP WITH 2 ACR'S AWAITING TKOF AT CVG.

Narrative

AS WE APCHED THE BEGINNING OF THE RWY WE WERE #1 FOR TKOF ON THAT SIDE OF THE RWY. THE ACTIVE RWY WAS RWY 27. WINDS WERE 080 DEGS AT 9 KTS. THERE WAS AN ACFT ON THE OTHER SIDE OF RWY 27 HOLDING BACK ABOUT 75 FT FROM THE HOLD SHORT LINE. ATC THEN TOLD US; OR SO WE ASSUMED; THAT WE WERE CLRED FOR TKOF; TURN R HDG 330 DEGS. WE READ BACK OUR CLRNC AND ENTERED RWY 27 FOR DEP. I WAS BUSY WITH CHKLISTS WHEN MY CAPT HEARD A CONVERSATION WITH THE ACFT ACROSS THE RWY THAT MADE HIM THINK WE ENTERED THE RWY BY MISTAKE. I ASKED FOR CONFIRMATION THAT WE WERE CLRED FOR TKOF AND ATC SAID; 'ARE YOU ON THE RWY?' I REPLIED; 'YES.' HE SAID SOMETHING LIKE; 'OK; YOU ARE CLRED FOR TKOF; TURN R HDG 090 DEGS.' THE WORD OK AND THE NEW HDG OF 090 DEGS INSTEAD OF 330 DEGS MAKES ME BELIEVE WE WERE NOT CLRED ONTO THE RWY AS I AND MY CAPT THOUGHT. DURING TKOF; I HEARD HIM CLR THE ACFT ACROSS THE RWY INTO POS AND HOLD. THE OTHER ACFT WAS FLT Y; WITH SIMILAR ALPHA NUMERIC. EVEN WHEN HE CLRED ACFT #2 ONTO RWY 27; I STILL HEARD OUR CALL SIGN. I BELIEVE THE NON STANDARD PHRASEOLOGY OF; 'OH'; THE LETTER INSTEAD OF 'ZERO' THE NUMBER; AND OUR ASSUMPTION WE WERE THE ONLY ONES AROUND WITH A CALL SIGN IN OUR NUMBER RANGE BOTH LED TO THIS POSSIBLE MISTAKE. WE CAN BE MORE ATTENTIVE IN THE FUTURE AND NOT 'ASSUME' ATC WILL TELL US SIMILAR CALL SIGNS ARE ON FREQ AND THE AGE-OLD PROB OF NON STANDARD PHRASEOLOGY COULD PREVENT THIS IN THE FUTURE.