Catalysis of the reaction: S-adenosyl-L-methionine(1+) + myo-inositol = 1D-3-O-methyl-myo-inositol + S-adenosyl-L-homocysteine + H+.
myo-inositol 1-O-methyltransferase (name based on 1L-numbering system and not 1D-numbering)