As a fun addition, I think the atomic clock/time standards division went HP → Agilent → Symmetricom → Microsemi → Microchip. You could have bought a HP 5071A Cesium Frequency Standard under all of these badges!
AT&T used to exist. Because it was a monopoly, it was broken up into the baby bells in 1982. One of which was Southwestern Bell, which eventually bought up all the other baby bells and what was left of AT&T. And then in 2005 it renamed itself...AT&T.