The reorder tone, also known as the fast busy tone, is the congestion tone or all trunks busy (ATB) tone of a public switched telephone network. It varies from country to country; in North America it is a dual-frequency tone of 480 Hz and 620 Hz at a cadence of 0.25 seconds on, 0.25 off; that is two beeps per second. It is used to indicate that an...