You can achieve call blocking by simply having a local tranmitter which saturates all the recievers,but because the phone bands tend to be in the 2 GHz plus range the safety concerns would make most manufacturers look twice at the idea.
I don't think you could really selectivly allow some types of calls and not others.
Ive got to say i agree with Craig if someone is so rude that they use a phone in a resturant or whereever then no amount of legislation is going make them into decent people.