Heath gets a lot of calls he doesn't want throughout the day. How can he block calls from people that aren't in his contact list, or send them directly to voicemail? Until recently, the FCC didn't allow carriers to do that, but carriers now have the ability to block calls. So the carrier could do this. But to block them himself, it isn't possible with an app because Apple doesn't allow alternate dialer apps. There are options for this on Android, however.
Leo says that Google Voice is the way to go. Google Voice will let Heath do exactly what he needs to do, but there's a question of what the future holds. Google Voice will act as a kind of receptionist that will screen the calls and tell him who's calling before he actually picks it up. Then he can choose whether to take the call or ignore it. Anveo is another interface that would let him program responses.