AIR CARRIER CLBS THROUGH CLRED ALT OF 4000 FT WHEN FO RPTR IS ASKED BY CAPT TO CONTACT COMPANY OPS; AND IS UNABLE TO BACK UP CAPT FLYING ACFT.

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WE WERE ON CLBOUT AND BEING VECTORED AFTER DEPARTING ABC ARPT. WE HAD LEVELED OFF AT THE APPROPRIATE ALT FOR THE SID AND CLB CHKLIST HAD BEEN COMPLETED. WE WERE THEN CLRED TO 4000 FT. PASSING 3000 FT THE STANDARD '1000 FT TO GO ' CALL WAS MADE AND ACKNOWLEDGED BTWN PF AND PNF. THE CAPT (PF) THEN INSTRUCTED ME TO CALL OPS. I STARTED TO TUNE THE OTHER RADIO AND WHILE DOING THIS; I NOTICED WE WERE GOING THROUGH OUR ASSIGNED ALT. I CALLED OUT THE ALT AND THE CAPT STARTED TO DSND BACK DOWN TO 4000 FT. MAX OVERSHOOT WAS 300-350 FT. ANOTHER ACFT WAS PASSING ALMOST DIRECTLY OVERHEAD AT 5000 FT. I HAD THE OTHER ACFT IN SIGHT SO THERE WAS NO DANGER OF COLLISION; JUST A LOSS OF STANDARD SEPARATION. IT NEEDS TO BE STRESSED TO FLCS THE IMPORTANCE OF THE STERILE COCKPIT RULES AND PROCS. IT WAS UNNECESSARY FOR US TO CALL OPS SO SOON AFTER TKOF. FOR WHATEVER REASON; THE PF OVERSHOT THE ALT; BUT MY STARTING OTHER CHORES DIDN'T HELP THE SITUATION; BECAUSE I COULDN'T DO MY REAL JOB -- BACKING UP THE PF. HAD I BEEN SOLELY MONITORING THE FLYING; THE OVERSHOOT WOULD HAVE BEEN MUCH LESS OR POSSIBLY WOULDN'T HAVE OCCURRED.