Yes, I understand that HylaFAX can be costly and lacks customization. Instead, consider ICTfax, an open-source solution with T.38/G.711 support and REST APIs. You can deploy it on EC2 with a SIP trunk to reduce costs while integrating seamlessly with your app. Building a custom T.38 service on EC2 using FreeSWITCH is feasible but it will require more VoIP expertise. AWS SaaS, like Chime SDK or APIs, may not meet your flexibility or budget needs. You can explore ICTfax further at ICT Innovations and test it for your use case.