As part of our mini-project to cover different aspects of WCAG 2.0 in a way that people can understand, this item helps people partake in events that are audio-only (no video). We've already covered adding captions to live video broadcasts here. This mandate is extremely similar, except sans video.
To keep this short and sweet, the best way to do this is to either purchase professional software that handles the live captioning, or by hiring a professional company to do it for you. There are several options listed here!
As always - if any questions, don't hesitate to reach out.