Called me at work and when I picked up it was a fax machine.

got multiple calls from this number...all tried leaving faxes on my 800 number

didn't leave a message, stayed on the phone for 1 minute.

Calls at least twice a day.  Two tones, but nothing else.  I suspect it is probing for a computer modem.  The two beeps means it is trying to electronically "handshake" and maske a connection.  It's an old hackers method. I have no idea why it keeps trying the same numbers.

It is not a fax machine as we have connected our fax machine on one of their calls and they call our number for or 5 times a day.  Very frustrating as you can not determine who they are.  Just a pain in the neck and very disruptive for a small business.