telephone exchange

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A central system of switches and other equipment that establishes connections between individual telephones.

from the GNU version of the Collaborative International Dictionary of English.

• A central office in which the wires of telephones from local subscribers may be connected by switches to other local telephones or to long-distance lines, to permit transmission of conversation or data.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun any equipment that establishes connections between telephones
• noun the building housing such equipment

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a workplace that serves as a telecommunications facility where lines from telephones can be connected together to permit communication