Don't see how that's relevant to the thread at hand. The problem here is that the Telco has an existing paying customer for a number, and has systems that allow

Don't see how that's relevant to the thread at hand. The problem here is that the Telco has an existing paying customer for a number, and has systems that allow other malicious actors to take over that number instead. It's not about verifying the absolute identity of the account owner, they only need to verify that the new SIM using a number has permission from the person who rightfully owns the account. In many cases, this fraud is being committed by employees of the carrier (e.g. at it's retail locations). That means the carrier clearly doesn't have adequate controls to prevent abuse.