A B757-200 DSNDING IN OAK; CA; AIRSPACE; ASSUMES DSCNT IS AUTOMATICALLY AUTH WHEN CLRED FOR AN APCH.

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WE WERE LEVEL AT 8000 FT MSL ON AN ASSIGNED HDG (APPROX 210 DEGS MAGNETIC) DURING THE APCH INTO SFO. I WAS FLYING AND THE CAPT WAS WORKING THE RADIOS. THE WX WAS VFR; WITH HIGH THIN CLOUDS AND VISIBILITY GREATER THAN 10 NM. APCH CTL HAD PREVIOUSLY ASKED IF WE COULD ACCEPT THE FMS BRIDGE VISUAL RWY 28R; TO WHICH WE REPLIED YES. THE CTLR NOW TELLS US TO MAINTAIN ASSIGNED HDG TO INTERCEPT THE FMS RWY 28R. THE CAPT READ BACK THE CLRNC. BOTH THE CAPT AND I WERE RELATIVELY NEW TO 'HIGH TECH' AIRPLANES. (I HAD APPROX 6 MONTHS EXPERIENCE AND THE CAPT APPROX 2 MONTHS.) SINCE NO SPECIFIC ALT RESTRS WERE GIVEN; I INTERPED THIS CLRNC AS ALLOWING US TO INTERCEPT THE FMS RWY 28R BOTH LATERALLY AND VERTLY. OUR HDG PUT OUR INTERCEPT POINT RIGHT AT ARCHI ON THE APCH. A FEW MOMENTS LATER; HE CLRED US TO 7000 FT AND TOLD US TO CONTACT THE FINAL CTLR. WE THEN SWITCHED OVER AND CHKED IN WITH THE FINAL CTLR. WE LEVELED OFF AT 7000 FT JUST PRIOR TO ARCHI. WITH VNAV/LNAV ARMED AND THE AUTOPLT ENGAGED; WE INTERCEPTED THE FMS RWY 28R APCH AT ARCHI INTXN. THE APCH SHOWS THE ARCHI XING ALT AT OR ABOVE 7000 FT. AFTER ARCHI; THE AUTOPLT FLEW THE LNAV/VNAV TRACK; STARTING A DSCNT TO CROSS TRDOW AT OR ABOVE 6000 FT. AT APPROX 6600 FT THE CTLR ASKED WHAT OUR ALT WAS. THE CAPT REPLIED 6600 FT AND DSNDING. THE CTLR SAID WE SHOULD BE LEVEL AT 7000 FT. THE CAPT STATED THAT WE HAD BEEN CLRED FOR THE FMS RWY 28R APCH. THE CTLR REPLIED THAT HE WAS THE ONLY ONE WHO CAN ISSUE THE APCH CLRNC. HE THEN IMMEDIATELY RECLRED US TO 6000 FT. A FEW MOMENTS LATER HE ISSUED US AN APCH CLRNC. WE WERE THEN HANDED OFF TO TWR AND CONTINUED THE APCH AND LNDG WITHOUT FURTHER INCIDENT. POINTS TO PONDER: 1) BOTH THE CAPT AND I THOUGHT THAT THE CLRNC TO INTERCEPT THE FMS RWY 28R APCH (A VISUAL PROC) WITH NO ALT RESTRS ALLOWED US TO INTERCEPT LATERALLY AND VERTLY. WERE WE INCORRECT IN THIS THINKING? 2) WHAT IS THE PROPER ATC PHRASEOLOGY USED FOR AN FMS APCH WHEN YOU ARE NOT TO DSND? FOR AN ILS APCH; IT USUALLY IS 'INTERCEPT THE LOC.' WHAT IS THE FMS EQUIVALENT PHRASE?