Blizzard will require Overwatch 2 and Modern Warfare 2 players to use SMS Protect, a 2FA system, to combat toxicity, but won't accept prepaid and VOIP numbers (Andy Chalk/PC Gamer)

Andy Chalk / PC Gamer:
Blizzard will require Overwatch 2 and Modern Warfare 2 players to use SMS Protect, a 2FA system, to combat toxicity, but won't accept prepaid and VOIP numbers  —  Just like Overwatch 2, you'll need to attach a phone number to your Battle.net account to play Modern Warfare 2—and prepaid phones aren't allowed.