From a search of Google I was able to discover that "TeamSpeak" is a VOIP voice communication software used by gamers to communicate while engaging in multiplayer games. There are web sites that discuss using TeamSpeak in Flight Simulator and in railroad simulation games such as MSTS and Trainz.
So I would conclude that it is just Trains Simulator 12 in multiplayer mode with the TeamSpeak software, as a separate system, controlling the voice communications between players. TeamSpeak requires a dedicated server to be setup before it can be used.
