The FAA has held, by legal interpretation by the FAA Chief Legal Counsel, that a phone call does not interrupt your rest period. Many pilots and pilot organizations have mistaken this interpretation to believe that it means the company may only call you once. This isn't what the interp says. It says a phone call doesn't interrupt rest.
By legal weight, the regulation, federal register preambles, and then FAA Chief Legal Counsel interpretations apply, and in that order. The legal interpetation is defensible in court and represents the official interpretation of the regulation as applied by the Administrator.