[hirsin]

It should be assumed they check the phone number provider and block twilio as a spam prevention technique.

[JoshMnem]

How can they detect Twilio numbers but still let scammers robocall my phone on a daily basis via bandwidth.com's API?

[jstanley]

Even where this doesn't happen, Twilio block messages of the form "Your Google verification code is 123456" so you can't receive them anyway.