got a call on my cell phone. i called back # but line was busy

The call you are receiving from that # is most likely and auto dialer. The beeps you hear is a fax tone waiting for receiving end to get connection tone.

Faxes that are sent are advertisements from companies looking for business.

I work for a company that constantly gets call from that # and we only get ads from the fax.

Agreed.  Number is unfamiliar, but no message left. I'm guessing Phishing company.

Same deal - picked up and caller hung up.. seems like an automated call.