THE ACFT DEPD MIAMI AT NGT ON AN ON-DEMAND, AIR TAXI FLT TO FT MYERS, FL. DURING ARRIVAL AT THE DESTN, THE FLT ENCTRD IFR CONDS. THE PLT OBTAINED CLNC FOR AN ILS RWY 6 APCH & WAS TOLD TO RPRT AT THE OUTER MARKER (OM). AT 0152:25 EST, HE RPRTD TO MIAMI CENTER THAT HE WAS OVER THE OM. THIS WAS HIS LAST TRANSMISSION TO AN ATC FACILITY. AT ABOUT 0203 EST, HE MADE A TRANSMISSION ON UNICOM FREQ TO INFORM ARPT OPNS PSNL THAT HE COULD NOT GET THE APCH LIGHTS TO OPERATE. HE WAS ASKED IF HE HAD USED THE PROPER FREQ & HAD KEYED THE MIKE THE REQUIRED NUMBER OF TIMES. THE PLT INDCD THAT HE HAD PROPERLY KEYED THE MIKE; HOWEVER, UNICOM PSNL DID NOT HEAR ANY KEYING OF THE MIKE EXCEPT FOR 2 CLICKS. THE ACFT CTCD THE GND IN A NRLY LEVEL ATTITUDE & WITH THE GEAR EXTENDED, APRX 1.5 MI SHORT OF RWY 6. IT THEN SKIDDED ABOUT 90 FT & HIT A TREE BEFORE COMING TO REST. NO PREIMPACT PART FAILURE/MALFUNCTION WAS FND WITH THE ACFT, ENG OR APCH/RWY LIGHTS. THE 0149 EST WX AT FT MYERS WAS IN PART: SKY OBSCURED, VIS 1/4 MI WITH FOG.