This one was an insurance broker, because I accidentally answered before checking ID (normally check ID first). I asked to be put on the DNC list and the guy got belligerent. So I gave it back to him, said I would report him to the FCC (he didn't care).
We generally never answer any call that is either an unknown number (or area code); an unknown cell number (especially with an out-of-state area code); a call with no recognizable (or welcome) name; or an "Anonymous" call. If it's important, they'll leave a message. If it's a telemarketer, they rarely leave a message.
Ever since moving to a new home and switching cable company back to Con-cast, we've received dozens of calls like this -- even though we are on the national and state Do Not Call registries. Fortunately, our Panasonic wireless phones have a Block Call feature that I use, after I search the number on 800notes. So, we are no longer bothered (except for the 1 ring we get - to let us know it is an attempted blocked call coming in.