Is prank calling illegal in the United States?

Besides being annoying it is illegal in most places. It would fall under "Harrassing Phone Calls" if it is non-threatening in nature.

It is a felony that could place you in jail for up to 2 Years. However you can never be charged with any crimes on the phone because the cops would have to prove that it was actually you on the phone.

some instances are illegal. check the link below and scroll down for the legality part to see more info.

On every call the Telco records the originating number and the destination number. If no one ever complains then it is a harmless prank. I know of houses in our area (outside the USA, but laws do vary from state to state) that cannot get Telephone service because there were prank calls made to people who did not like to be annoyed. In one case the people that moved into the house had to pay a deposit that was quite large, and they were warned that if there were complaints of prank calls that they would lose their service again and their deposit. I believe that they had to provide some proof to the police that they were not in the area while the calls were being made. The deposit was applied to their phone bills, until it was used up. What is a prank to some people is an unwanted annoyance to others. I know people that think it is funny to mush a pie in someone's face, or to soak people with cold water, the people on the receiving end do not always think of it as a prank.