THE EN ROUTE PORTION OF THE FLT WAS UNEVENTFUL, EXCEPT THAT THE PLT USED THE CALL SIGN 'N251DE' INSTEAD OF 'N33670' WHICH WAS THE REGISTRATION NUMBER OF HIS ACFT. DRG ARRIVAL AT BOSTON, HE WAS PROVIDED RADAR VECTORS, CLEARED FOR AN ILS RWY 4R APCH & INSTRUCTED TO CONTACT THE TOWER. THE PLT CONTACTED THE TOWER & RPRTD OVER THE OUTER MARKER. SHORTLY THEREAFTER, THE ACFT ENTERED A LEFT TURN, THEN RADIO & RADAR CONTACT WERE LOST. IT CRASHED ABOUT 2.5 MI SSE OF THE ARPT.A WITNESS NR THE CRASH SITE THOUGHT THE ACFT HAD ENG PROBLEMS WHEN HE SAW IT DSCNDG IN A WESTERLY DIRECTION. HE SAID THE ENG THEN 'SMOOTHED OUT' & THE PLANE BGN TO CLIMB, THEN IT SUDDENLY WENT INTO A DIVE & CRASHED. DRG IMPACT, THE ACFT STRUCK A RESIDENCE & A PARKED AUTO. THREE HOUSES & 10 AUTOS WERE DESTROYED BY IMPACT & FIRE, OTHER HOUSES WERE DMG BY FIRE. NO PREIMPACT PART FAILURE OR MALFUNCTION WAS FND. THE PLT WAS CONDUCTING PART 135 OPNS IN IFR WITH 545 HRS TOTAL FLT TIME, 59 HRS INSTRUMENT TIME & 95 HRS NGT EXPERIENCE.