FUNCTION CHECK_TEL_FORMAT (PTELNO VARCHAR2) RETURN BOOLEAN IS
OK BOOLEAN := TRUE;
CH CHAR;
BEGIN
OK := TRUE;
IF PTELNO IS NULL THEN
--MSG('Lütfen telefon numarasini giriniz...');
--OK := FALSE;
null;
ELSE
IF LENGTH(PTELNO) != 10 OR SUBSTR(PTELNO,1,1) = '0' THEN
OK := FALSE;
END IF;

IF OK THEN
FOR I IN 1..LENGTH(PTELNO) LOOP
CH := SUBSTR(PTELNO,I,1);
IF CH NOT IN ('0','1','2','3','4','5','6','7','8','9') THEN
OK := FALSE;
END IF;
END LOOP;
END IF;

IF NOT OK THEN
MSG('Lütfen telefon numarasini 10 hane ve sayisal deger giriniz...');
END IF;
END IF;

RETURN OK;
END;