Freeview TV is Digital Television through a conventional roof-top aerial. For this technology, new digital TV adapters, as well as integrated digital TV sets (IDTV), are available on the market, without any obligation to subscribe to pay TV unless you wish. Digital terrestrial transmission is designed to work, in the main, with existing roof-top aerials in good condition, but some households will need a new roof-top aerial. It depends on several factors, especially:

Where you live
Which frequencies are used at your local transmitter

The nature and condition of your current aerial installation