With the advent of OSPS a feature called Interflow allowed operators on a system to answer calls from anywhere within their region. As technology changed, so did the application of Interflow. Interflow was implemented nationwide by AT&T. This allowed AT&T to close virtually every operator office throughout the US. As of 2004 the only AT&T operator offices remaining were located in Houston, Texas, and Jacksonville, Florida. Operation The switchboard is usually designed to accommodate the operator, who sits facing it. It has a high back panel, which consists of rows of female jacks, each jack designated and wired as a local extension of the switchboard (which serves an individual subscriber) or as an incoming or outgoing trunk line. The jack is also associated with a lamp. On the table or desk area in front of the operator are columns of 3-position toggle switches termed "keys", lamps, and cords. Each column consists of a front key and a rear key, a front lamp and a rear lamp, followed by a front cord and a rear cord, making up together a cord circuit. The front key is the "talk" key allowing the operator to speak with that particular cord pair. The rear key on older "manual" boards and PBXs is used to ring a telephone physically. On newer boards, the back key is used to collect (retrieve) money from coin telephones. Each of the keys has three positions: back, normal and forward. When a key is in the normal position an electrical talk path connects the front and rear cords. A key in the forward position (front key) connects the operator to the cord pair, and a key in the back position sends a ring signal out on the cord (on older manual exchanges). Each cord has a three-wire TRS phone connector: tip and ring for testing, ringing and voice; and a sleeve wire for busy signals. When a call is received, a jack lamp lights on the back panel and the operator responds by placing the rear cord into the corresponding jack and throwing the front key forward. The operator then converses with the caller, who informs the operator to whom he or she would like to speak. If it is another extension, the operator places the front cord in the associated jack and pulls the front key backwards to ring the called party. After connecting, the operator leaves both cords