Companies that file 10K and 10Q reports with the SEC satisfy this requirement. The filing is effective for 90 days. If the seller wishes to extend the selling period or sell additional securities, a new form 144 is required. The sale of the securities may not be advertised and no additional commissions can be paid. If the shares have been owned for two years or more, no volume restrictions apply to non-insiders.
Insiders are always subject to volume restrictions.
The most recent rule change of Feb 1997 reduced the holding periods by one year.