Does Google Talk or GTalk support real-time text (RTT)? If it does is there any example or a snippet of it somewhere? I have seen the proposal of Mark Rejhon, but didn't find any solid proof that GTalk supports RTT.
Try it now - it works over Google's server. Just log on using your GMAIL account & your existing buddy list shows up, and you can chat RTT right away. Google's own GMAIL client does not support RTT, but Google's Talk Servers supports RTT well. A properly implemented XMPP network (jabber.org) supports RTT too. So that means any third-party software (supporting XEP-0301) can implement it. You just log on using your Google Talk ID or Jabber compatible ID.
No server modifications are needed; it's a client based protocol that works perfectly through Google Talk's own servers. The RTT goes through the existing Google Talk servers as extension data; via the same network routing as existing XMPP messages (Google Talk message delivery).
If you try to chat between an RTT client (e.g. Gallaudet or RealJabber) and Google Talk, the line-by-line messages make it through, the typing just doesn't show up in real-time.
P.S. The standard is being upgraded from Experimental in the near future.