I'm afraid mobile devices do not currently have this capability -- only the GoTo desktop apps. I will leave this up as an 'idea' for future enhancement considerations.
This would be great, as the chat functionality is a great possibility for long running actions to keep everyone up to date. A chat for status updates on a migration weekend in IT for instance.
Also super would be to see past chat messages if a participant joins later. So he is two hours late but can still catch up by reading the past messages.