No, the planes did not knock the Twin Towers down. They collapsed minutes after the planes hit and some are still skeptical as to why the collapses happened.

Automobile radio antenna come in a variety of different configurations, including but not limited to: telescoping masts, fixed masts, and antenna that are molded into the windshield.

A transmission tower is the center of all radio braodcast stations.

when you dial a number in your cell phone, the call does not go from your phone to the other person's phone. The call is able to be made by a series of transmission towers the form the comunications area of coverage. Radios work the same. if you are in a long drive the radio station might get off the air and you will pick another one in the other state.
In the related links box below, I posted the wikipedia article on Radio Masts and towers for more information.

Don Daso has written:

'Antenna towers for radio amateurs' -- subject(s): Antennas (Electronics), Radio and television towers, Radio, Amateurs' manuals, Design and construction

Metal towers can be called structures like radio towers, transmission towers, or lattice towers, depending on their specific function and design.