For async text, surely basic email would suffice? Or phone text, skype, linked in, or this RG site messaging would also work ok. Hook up with your participants on a dating site and grab the ensuing message thread (this has ethics risk). Or to be novel, you could even blend retro and email a scanned written letter! All would be legally valid documents. So, there are many existing ways to gather async text. Are you desiring something more from these existing tech platforms in gathering your async text data? With voice, you would then probably need to then transcribe anyway, so no suggestions there. Hope that helps.

Thank you Karl J. Matthews there is a lot of options on your answer for me to search!