I get marketing calls all the time on my cell phone and notice the same thing - multiple inbound numbers from the same organization. Sheesh!!
I stash the numbers under a contact name Do Not Answer A - B - C, etc. - 5 numbers per contact. I set up a Silent ring tone for these contacts. If subsequent calls come in from the number(s), I don't hear it and I don't get docked minutes for the call. It's rare that any of them leave a message.
Bill
