The proper thing to do is to complain to Charles Schwab that you want a corrected consolidated 1099 that reports interest and associated premium on the same form (either 1099-INT or 1099-OID allow it).
While waiting forever for them to agree to do so, the best way to get proper calculation of net interest is to 0 out flagged premium value on 1099-OID and to Adjust interest reported on 1099-INT as described elsewhere (see my replies above and below for more details. Please tell Charles Schwab that they should not make you do all this work yourself.
