Is there an open-source or paid SDK/API that I can use to create a group voice chat mobile app with "live" transcription? Or something that can plug-in to a system like this? I looked at Twilio but they seem to only offer a means to do it on their VOIP/SIP product.
Yes, Google, Amazon, Microsoft all offer streaming solutions (wouldn't recommend Amazon's however, might recommend Microsoft over Google). wav2letter from FB is the only open-source framework worth looking at, deepspeech is not a seriously usable framework.