It looks like there are 2 versions: 1 Universal and 1 iPad-specific. If I had 1 copy of the universal and synced it with my son's iPhone, my wife's iTouch, and my iPad, will we be able to play 1 common session in our living room? Will the universal work with the HD version?
You can play on the iPad version, with others who are using the iPhone version. My daughter and I did this before she got her iPad. Once she did, we got the tile rack program for the iPhone and play that way too....a lot of fun!
If you are all connected to the same WiFi network you just hit Local Network play.