You can't duplicate your SIM, but your phone carrier can. In some countries, this involves them checking your government-issued ID in person, which is handy for

You can't duplicate your SIM, but your phone carrier can. In some countries, this involves them checking your government-issued ID in person, which is handy for Google as a way to outsource the ID-checking requirements. The issue is that they don't discriminate between carriers that perform good identity checking and those that don't. (Reliability is actually well-addressed by Google - they offer this as a supplement to the other forms of verification they provide.)