It's not Twilio; it's a combination of Telnyx and Signal wire and a link trip not using their TTS & STT. I'm using a combination of Cartesia and the self-hosted misolabs for TTS. I'm using Deepgram and in some cases Sarvam as well. It's a combination of all these things.

As far as the question is why I used Telnyx and SignalWire, it's because of the cost and the latency thing. The Twilio API is not really fast as far as I've used it. I don't know about other people. I didn't find anything as such on the internet but I've used and tested both Telnyx and SignalWire. The best one is literally Telnyx but it is costly compared to SignalWire. In order to make a profit on that I had to use a combination of both.