The area code 543 is not currently in use in North America. The closest existing area codes to this one numerically are 541 for Eugene, Oregon, and 551 for Newark, New Jersey.
Area codes are administered and handled by the North American Numbering Plan Association, or NANPA. What people usually call area codes are officially known as NPA codes. Any set of three digits (000-999) is theoretically an area code, but at this time, only 316 of these codes are in use. In addition, some codes are saved as special markers of some sort. For instance, the 800 area code is used for "toll-free" calling, where the recipient pays for the call rather than the caller.