Very interesting, for people who want to create multiple emails or maybe register themselves on telegram or facebook. I don't think it's a big deal if someone buys your services, considering that you seem to buy a new phone number that hasn't been used before. Surely the number you buy is unique.

Btw... How long can you keep that number for your customers? And if I want to use it again for the second time, will I get charged again?
For example, today I bought a number to verify Facebook and Telegram, can I still use the same number one week later to verify my Twitter or WhatsApp account?