Which standard specifies the AT&W AT command?

Question

While discussing how to process AT commands with a colleague, we discovered that contrary to our belief the command AT&W (store user profile) is not specifi

Answer 1

What you're looking for is called the Hayes command set, popularized by the Hayes modem. It was a "de facto" standard long before it was adopted by V.250.

Wikipedia has a brief description and history, and Microsoft has a summary of the command set.