The solid phases of methanol were investigated using IR spectroscopy and numerical calculations with the SIESTA method. Improved spectra are reported of amorphous methanol at 90 K, and in particular of the alpha and beta phases at 130 and 165 K, respectively, with assignments of bands not previously measured. The main features of the spectra of each phase are discussed and compared. A study of spectral changes with temperature leads to the conclusion that the metastable phase previously reported might be a mixture of the two known stable phases. Such a mixture could explain all spectral features observed in this investigation. The theoretical calculations provide reasonable agreement with the experimental data for most of the parameters, but predict H-bondings stronger than those observed. Differences between the spectra of the alpha and beta phases are predicted with similar characteristics to the experimental results.