NMAC BTWN A BEECH 55 THAT JUST COMPLETED A TURN ONTO FINAL AT A NON CTLED ARPT AND A CESSNA THAT TURNED FINAL IN FRONT OF HIM. THE RPTR IN THE BE55 TOOK EVASIVE ACTION BY TURNING OUT OF FINAL.

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AFTER CANCELING IFR WITH ATC; I SWITCHED TO UNICOM FOR ST SIMONS ISLAND; GA (1J1). AS I ENTERED THE AREA; I ANNOUNCED DISTANCE; DIRECTION; AND LNDG INTENTIONS. I ASKED FOR ANY OTHER TFC TO 'ANNOUNCE' ALSO. A COUPLE OF ACFT ANNOUNCED THEIR POS WITH ONE STATING THAT THEY WERE MAKING A PRACTICE VOR APCH. I CONTINUED INTO THE TFC PATTERN MAKING ANNOUNCEMENTS AT EVERY LEG; INCLUDING XWIND. SHORTLY AFTER LEVELING WINGS FOR FINAL; A CESSNA TURNED IN FRONT OF ME ROLLING OUT FROM BASE TO FINAL JUST INSIDE AND SLIGHTLY BELOW ME WITH NO ANNOUNCEMENT. I TURNED 90 DEGS R (HIGH BANK ANGLE); ADVANCED THE THROTTLES; AND DSNDED. THEN ROLLED BACK TO THE L (90 DEGS) AFTER A FEW SECONDS TO PARALLEL THE FINAL COURSE AS I WATCHED THE CESSNA DSND TO LNDG. THERE WERE SOME TERSE WORDS FROM ME OVER THE RADIO TO ANNOUNCE WHAT HAD HAPPENED. THE OTHER PLT WAITED FOR ME ON THE GND WHERE WE 'COMPARED NOTES.' HE WAS A 12000 HR AIRLINE PLT INSTRUCTING AN INST STUDENT IN A VOR APCH. HE THOUGHT HE HAD ANNOUNCED AND HE DID NOT HEAR ME. HE HAD NOT ANNOUNCED AND EVERYONE ELSE DID HEAR ME; INCLUDING THE FBO ON THE GND. WHEN HE REALIZED THAT HE HAD ALMOST CAUSED AN ACCIDENT; HE APOLOGIZED PROFUSELY AND QUICKLY LEFT. 1J1 IS 'UNCTLED' BUT IT IS AN EXTREMELY BUSY RESORT DEST WHERE A GULFSTREAM V IS AS LIKELY TO LAND AS A C172. PRACTICE APCHS SHOULD PROBABLY NOT BE MADE AT THIS TYPE OF ARPT DURING PEAK WKEND HRS. (ANOTHER ARPT EXACTLY LIKE IT; IS DESTIN; FL; WITH WHICH I AM EVEN MORE FAMILIAR.) IN THIS CASE; THE INSTRUCTOR AND STUDENT WERE APPARENTLY SO ENGROSSED IN THE APCH THAT THEY DID NOT COMMUNICATE OR PERHAPS THEY HAD INADVERTENTLY SWITCHED FREQS AFTER RESPONDING EARLY ON. ANOTHER ISSUE IS THAT WHEN AN ANNOUNCEMENT IS MADE USING AN 'APCH' AS A LOCATION ON A VFR DAY; OTHER TFC MAY NOT BE FAMILIAR WITH WHERE THAT MAY PUT THE TFC. AT THAT POINT; IT IS TOO LATE TO REFER TO THE CHARTS.