SMA PLT TAXIES WITHOUT CLRNC BELIEVING TWR CLOSED.

Narrative

I HAVE FLOWN OUT OF WILLIAMSPORT; PA; SEVERAL TIMES BEFORE; AT EARLY HRS JUST BEFORE THE TWR OPENS. I WAS ALWAYS UNDER THE ASSUMPTION THAT THE TWR OPENED AT XY00 LCL TIME. SOMEONE EVEN TOLD ME IT WAS XY00 WHEN I INQUIRED. I STARTED THE AIRPLANE IN TIME TO HEAR A COMMUTER'S REPEATED CALLS FOR AN IFR CLRNC; WHICH LED ME TO BELIEVE THE TWR WAS CLOSED. SO ; I BEGAN TO TAXI AND ANNOUNCED I WAS XING RWY 12/30 ON CTAF. IT WAS THEN THAT THE TWR CTLR STOPPED ME AND TOLD ME THAT THE TWR OPENED AT XX30 LCL TIME. I TAXIED WITHOUT A CLRNC AND ALMOST HAD A RWY INCURSION. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR WAS CALLED AS HE IS A CFI AND THERE WAS CONCERN THAT HE WAS NOT USING OR TEACHING THE USE OF ARPT FACILITIES DIRECTORY. HE ACKNOWLEDGED THAT HE KNEW OF AN USED THE ARPT FACILITIES DIRECTORY BUT HAD ASKED THE FSS PERSONNEL WHEN THE TWR OPENED AND WAS TOLD XY00 AM. HE ALSO ASKED THE LINE PERSON IF THE TWR OPENED AT XY00 AND THE RESPONSE WAS 'AS FAR AS I KNOW.' WELL; THE LINE PERSON IS OBVIOUSLY NOT THE PERSON TO ASK. RPTR NOW KNOWS HE MUST CHK FOR HIMSELF.