Mobile Phone verification method

1. Probably not a good idea to give a forum your phone number. One because of security, second because of governments.
2. Would restrict or make harder for people to join, why would I want to give my phone number to some shady leaking forum?
3. We would probably have to invest in some service which would cost us.
4. There are free and paid phone number account confirmation services online.
5. It's not that hard to buy a sim for like $5 in your nearest Walmart or w/e.