B737 First Officer reports missed instruction to cancel takeoff prior to and during takeoff roll. Reporter believes noise canceling headsets with one ear uncovered for cockpit communication is the reason for the missed communication.

Narrative

We were cleared for takeoff by Tower. After starting the takeoff roll (my takeoff) we heard a partial radio transmission about aborting a takeoff. At this time the power was set. I said; 'What did he just say?' The Captain only heard part of the transmission also. The Captain asked ATC. Tower replied; 'Abort your takeoff if you can do so safely.' The Captain immediately took control of the aircraft and accomplished our RTO procedure. We accelerated to about 70 KTS. After clearing the runway I asked Tower; 'What was that all about?' They said they tried to cancel our takeoff clearance before we started our roll but we didn't respond. The Captain later called Tower on the phone and they said there was a traffic conflict at a near by airport that caused them to have to cancel our takeoff clearance. As a note: We were both wearing noise cancelling headsets; but in order to hear each other; we still have to have one ear uncovered. This obviously compromises the noise cancelling capabilities. I truly believe that if we had a hot mic interphone we could wear the headsets the way they were intended to be worn covering both ears and increasing our capability of hearing VHF radio transmissions much more clearly.