does your girl friend ever have her modem set to receive calls, if so than she could be on a list from a war dialer.

but i agree, its most likely a fax.

if you really want these calls to stop, set up her machine to receive faxs, let it receive the message. most faxs have the sending phone number on them, so fax them back telling them to change their number.

if they call again and can't connect then you know its not a fax and you might learn something using telix. caller id might be useful.