There is a commercial offering for Avaya SIP trunks, See this doc.
In a pinch if we needed some trunks for a customer, we have used Avaya CPaaS for SIP trunks. This is (so I have heard) the equivalent of a Twilio SIP trunk.
You can claim a number in less than 10 minutes, and provision the IPO in as much.
First, let’s set up the SIP trunk and grab a new number. Go to cloud.zang.io.
CREATE A DOMAIN
From the dashboard, go to SIP>DOMAINS.
Click on Create SIP Domain
Assign the domain name. The Domain name you enter will prepend the “sip.zang.io”. Give the Domain a friendly name.