You only need a converter box if you get your television via over-the-air broadcast and don't have a digital tuner built in. If you get your television via cable (with a cable box or no), satellite, FiOS, U-Verse, etc., you don't need a dtv converter box. On Feb. 17, nothing will change for you.
If you get OTA broadcasts, and you're unsure if your television needs a box, if you have the ability to type in a hyphen or decimal point in the channel number on your TV, you hava digital tuner. Fo example, in the Los Angeles area market, if you can type in 11.1 (11-1), you will get Fox in both digital and HD via OTA broadcast. Your best bet if your'e unsure, however, is to look up if your TV has a digital tuner online on the equipment manufacturer's website.