DC9-40 CREW FORGOT AN ATC ASSIGNED ALT XING RESTR IN ZNY CLASS A.

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IN CRUISE FLT; ON BUNTS 1 ARR INTO PHL; GIVEN CLRNC TO PROCEED DIRECT TO HAR AND CROSS 40 MI W AT FL250. FO ACKNOWLEDGED CLRNC WITH ATC. SET 25000 FT IN AWI AND CALLED IT OUT. CAPT RESPONDED WITH ALT CLRED TO AND XING FIX. CAPT PICKED HIS DSCNT POINT AND CONTINUED WITH PF DUTIES. CAPT AND FO STARTED TO LISTEN TO ATC CONVERSATION WITH ANOTHER ACFT. CAPT CALLED FLT ATTENDANT AND ASKED FOR COFFEE. DURING THIS TIME FO WAS PERFORMING APPROPRIATE DUTIES; UPDATING PHL ARR ATIS. CAPT OPENED COCKPIT DOOR AND RECEIVED HIS COFFEE. WITHIN MINS ATC ASKED US IF WE WOULD MAKE THE XING RESTR. THIS OCCURRED AT 44 DME W OF HAR. CAPT STARTED DSCNT; IDLE AND BOARDS; AND DIRECTED FO TO TELL ATC WE WERE BEGINNING DSCNT BUT WOULD NOT MAKE XING AT FL250. NO RESPONSE FROM ATC. AT 40 DME CAPT DIRECTED FO TO TELL ATC THE XING ALT (FL275); NO RESPONSE FROM ATC. WE WERE LEVEL AT FL250 AT 36 DME. CAPT DIRECTED FO TO RPT LEVEL AT FL250. NO RESPONSE FROM ATC. MOMENTS LATER ATC GAVE US A FREQ CHANGE AND WE CONTINUED ON THE ARR TO PHL. THE CREW ALLOWED THEMSELVES TO BECOME DISTRACTED WITH AN ATC CONVERSATION THAT DID NOT CONCERN OUR FLT. THE CREW WAS ALSO DISTRACTED BY OPENING AND CLOSING THE COCKPIT DOOR WHICH HAD BECOME A 2 PEOPLE JOB WITH THAT NEW XBAR INSTALLED. WE ARE NOT SURE AT WHAT POINT WE FORGOT THE DSCNT CLRNC; BUT WE WERE RAPIDLY BROUGHT BACK TO WHAT WE SHOULD HAVE BEEN DOING WITH ATC'S CALL.