The hold button was invented in 1962 apparently (
http://wiki.answers.com/Q/Who_invented_the_hold_button )
The automated attendant was patented in 1988. So they probably didn't really become popular until the 90s. This was the first system that used "press one for Marketing, two for Accounts payable" etc. Answering machines have been around a lot longer (first answering machine was invented in 1935) but your calls couldn't be automatically routed to another line. Centrex and PBX systems (late 50s early 60s) allowed for call forwarding, call parking, call pickup and hunt groups (if the primary line is busy, the call "hunts" to the next available line in a group; if all lines in a hunt group are busy, the caller gets a busy signal). Mostly very large organizations, businesses with multiple locations or governmental agencies used these type of systems before the 70s.
AmyN
