Originally Posted by xJumper
They might as well be using your MSN or ICQ# then because that does little in terms of deterrent/security especially if your goal is to somehow avoid repeat hackers/cheaters re-registering. You can basically buy as many phone numbers as you want today using various services.
Then, if giving them one's number isn't ideal, one can do so using said services. It's either a good deterrent or a non-issue.
In any case, it's more a deterrent than having no other system in place. The aggregate (VAC, community review, and phone number) is decent and is more than a lot of other games do in regard to cheat prevention. I mean, if you're already on Steam, the 3 step verification is advisable.