i believe this is how it works: they are routing +888 toll numbers through their own infra to accept calls from the telegram 2FA service and then securely send you a login code after authenticating with your wallet. the numbers are NFTs on the TON blockchain.
it seems like they purchased the +888 area code from the International Telecommunication Union. it was previously used for Telecommunications for Disaster Relief https://en.wikipedia.org/wiki/Telecommunications_for_Disaster_Relief