HI jsaad

Advantages of SBCs:
1.IP blacklist can be set.
2.Traffic, registration statistics and call records through SBC
3.Check domain names first.(Not a public domain, more like passphrase)
4.SBC can be behind a Router or directly on the public network

This will be the reason why I recommend SBC.
In our country, the IP telephony system is often challenged by customer's IT.