On another forum, someone stated is was a telemarketer affiliated with Canadian Pharmacy..  The only way to tell for sure is to have the phone company set up what is called a trap.

The Trap allows the phone company to determine the telephone number from which the harassing calls originate. You must keep a log noting the time and date the harassing calls are received. Traps are usually set up for no more than two weeks. The phone company does not charge a fee for Traps.

The Phone company actually has to trace the call log through which physical trunk the call come on.