I have seen something like this in my Inbox… “Possible Phishing Scam”… Pretty handy! The same idea works on your smartphone… just tap the (i) (in a circle) and then touch either Create New Contact or Add to Existing Contact to add a telemarketers number to a “SPAM” contact in the iPhone address book. That way I never answer them a second time! There does not seem to be a limit to the phone numbers I can add to my SPAM contact.
BTW: There is a place you can report telemarketers as SPAM and share the knowledge on several sites. Just type the number in your browser URL address box; you can also see what others may have already posted about the number as well.