I have a suggestion for an upcoming version of iOS for the iPhone: let's have a Junk Call button for your phone. Wouldn't it be great to have a button that allows me to send a sales call to a junk call folder?
Any further calls from that number get handled a specific way (e.g. no ring, just disconnect the call or send the disconnected or no longer working tones to the caller). In other words, it would handle things much as the late, lamented PhoneValet did on the Mac.