Most area codes of the form N10, originally reserved for AT&T's Teletypewriter eXchange (TWX) service, were transferred to Western Union in 1969 and were freed up for other use in 1981 after conversion to Telex II service was complete. The last of these, 610, was assigned to Canada, but reassigned in 1992. These new area codes, as well as a few other codes used for routing calls to Mexico, were used for telephone area code splits in the late 1980s and early 1990s, as all other area codes under the original plan had been consumed.