There is a piece of software called 'Roger Wilco' that allows streaming audio between users, i.e. they can talk to each other in real time. In know online gamers use it, as do the world of virtual airlines.
Maybe there is a website geared up for RT practice between pilots/ATCO's/anyone else who wants to practice. If not, could be good opp to start one...
Anyway, I think its a free download and there are also forums where people can talk to each other instead of using electronic posts. I'm sure it would be quite easy to start up an RT practice room.