Certs are first for the server to prove its identity to the client. That's the same for SBC to phone or Amazon.com to Chrome.
If you're in a highly secure environment, or inside an enterprise with all the machines - cell phones included - joined to a domain with identity certificates, you can use peer verification/mutual TLS authentication.
That way, your SIP remote worker setup won't esablish a handshake with the client unless the client in certmgr.msc has an identity certificate provided by the company for them. Then, you'd be trusting the company's CA cert in the server profile. That way you'll never get INVITE:01145411231231232132@yourPublicIP coming into your SBC - the hackers don't have a cert issued by TheCustomer.com's private internal CA.
You can use that, but as a pre-requisite you'd have to have all the endpoints with an identity cert. If the deployment use case was laptops for work from home but those laptops are joined to the domain or otherwise administered centrally, then it's as easy as you adding the company CA cert to trust for peer verification.
But we don't want to get too far into that - give them the MSI for IX Workplace, let them automate deployment of the client, use Zang to autoconfig based on email address to AADS and you're done as far as managing end user client configurations. If they already have identity certs on each machine and want to bring it to the table, sure, but they've already done the heavy lifting.
Don't forget to read and follow the security best practices for 8.0