I really don’t think this is related to the Callback feature. The requirements for Bnet accounts overall have changed.
Recently people have posted here for help because they can’t set up the mobile authenticator without a valid phone number - which should NOT be the case. Auth is supposed to work even on non-phone devices and is not linked to SMS Protect.
This thread explores the back and forth between folks here on the CS forum with a user trying to figure out why it was asking for phone number to set up Mobile Auth. Can't use authenticator
Today I noticed the login screen for WoW asks for Email (normal) OR Phone Number
There are LOTS of threads on the Blizzard forums https://us.forums.blizzard.com/en/blizzard/ related to Invalid Phone Numbers.
Today looking at the Invalid Phone Number article it is no longer an OPTION to use a phone number for some users - especially if you want to play free games. https://us.battle.net/support/en/article/202594
This is heavily impacting Activision users it seems (as was maybe the intent?) but the trickle down is that that it now impact Blizzard folks setting up Authenticators, logging in, and now making tickets.
There are many reasons a Phone number can be considered invalid by the system - if it was once pay by minute, VOIP, Cricket, or if your country on the account does not match the phone number. Very few of those can be changed and the phone number lockout can’t be over ridden by CS.
I am really hoping that the new Login Screen asking for Phone number OR Email is not indicative that a phone number is going to be required for all Blizz accounts.