Use HTTP for client-server communication. So you can simply use Servlets, Jsp or even PHP for the server side, which can be used on cheap rentable servers. You will also avoid firewall and proxy problems this way. A poker game is even possible to completely run on the server and just deliver html-pages to the browser.
This is one solution buti believe its a little hard, and running all the game in the server i dont think its effeciency. Anyway i was looking something like a game engine or a framework to start builfing on this.