A modem test command. Not much more.
Here on the west coast of the USA (aka "left" coast), it WAS "Pacific Telephone", part of the original AT&T. Then came 1984. Became "Pacific Bell". Got a baseball park named after it. Then bought out by SBC (aka "some big company"). Renamed the ball park. Then they bought (what was left of) AT&T, the old long distance company. Took on the name.
Of the "Baby Bells" (NYNEX, Bell Atlantic, Bell South, Southwestern Bell Company, Ameritech, US West, Pacific Telesis), 4 are now under the new AT&T umbrella. Two (NYNEX, and Bell Atlantic) along with GTE (Great Telephone Experiment) now are Verizon. The only thing left is US West, now "Qwest communications". Who knows if/when it will be swallowed up (but it does have the largest (area) territory).
So concludes our telephone history lesson for today. See how well anti-trust breakups work!