A B727 FLC ACCEPTED A DSCNT CLRNC IN ERROR. ACFT CAME WITHIN 2 PT 5 NM OF ANOTHER ACFT.

Narrative

I WAS TRYING TO OBTAIN ATIS FROM EWR. DUE TO THE LARGE VOLUME OF ATC CALLS; THE INTERMITTENT RECEPTION OF EWR ATIS; AND THE CAPT/FO REQUEST TO RECEIVE ATIS ASAP; DUE TO UNFAMILIARITY OF ARPT AND RWY IN USE (FOR BRIEFING); I TURNED DOWN ATC VOLUME TO TRY AND OBTAIN EWR ATIS. WHILE ON DSCNT FROM FL190; THE EWR ATIS WAS STILL COMING IN BROKEN. AT APPROX 12500 FT WE RECEIVED A TCASII ADVISORY AND I LOOKED UP FRONT TO SEE OUR ALT AND THE INTRUDERS ALT/DIRECTION. THE INTRUDER WAS OBSERVED AT THE 12 O'CLOCK POS GOING TO 11 O'CLOCK; AS WE LEVELED OFF AT 12200 FT. AT THAT SAME TIME I TURNED MY ATC VOLUME BACK UP AND LISTENED TO THE CTLR ASK US TO CLB TO 13000 FT. AT THAT POINT THE CAPT/FO BRIEFLY DISCUSSED THE SIT AND THE CAPT THEN BRIEFLY DISCUSSED THE SIT WITH ATC. I THEN CONTINUED TO TRY AND GET ATIS BUT WAS UNABLE TO CLRLY RECEIVE EWR ATIS UNTIL WITHIN 50 NM OF EWR AT 10000 FT. CONTRIBUTING FACTORS: EXTREMELY BUSY FREQ WITH LIKE SOUNDING CALL SIGNS TO OUR OWN. SUSPECT THAT IS WHERE 10000 FT NUMBER CAME FROM. COULD NOT RECEIVE ATIS WITHIN 50 NM; CAUSING SO TO BE OUT OF LOOP. ARR CHART EXPECT ALT OF 7000 FT IN FRONT OF US CONTRIBUTING TO THE ASSISTANCE OF 10000 FT BEING A REASONABLE ALT. SUBCONSCIOUS CORRELATION OF 10000 FT AND 250 KTS. NO CTLR READBACK ACKNOWLEDGEMENT OR CORRECTION OF OUR ACCEPTANCE. SUGGESTIONS OF HOW TO PREVENT RECURRENCE: ATC ACKNOWLEDGEMENT/CORRECTION OF ALL ACFT ALT READBACKS. ACARS ON ALL ACFT IN ORDER TO RECEIVE DIGITAL ATIS DURING CRITICAL PHASES OF FLT.