My question is this: What happens if you use Authy but you lose both your phone and with it your phone number (pay as you go simcard)?
This has been worrying me for a long time now and I am hesitant to use it.
Just call up your service provider and get a new sim shipped out. I wouldn't use a burner phone for this so if you're going to use one make sure you can easily get a replacement sim sent out in case you do lose it.
You can associate an email address to your account which will help you or you can use 'inherited trust' feature.
Have you tried 'master recovery codes' to change number? I think it works.
http://blog.authy.com/multi-deviceDoesn't this kind of defeat the purpose of the app if you can just bypass it with email? That makes your email address a hot target for hackers and a way they can easily bypass 2-factor.