It's just a trademark for GT4 Mobile online mode. If you remember developer Polyphony Digital hinted that they would now be aiming to reform the game at its core to provide something that's not available at home. Well that "something" is a big "something", as it will now contain a tentatively titled "Hello World" online mode, complete with all strings, bells and whistles. GT4 Portable will now be the flagship title Sony has to roll out its online PSP plan. This will offer something entirely unique that will draw even people who own the console GT4 to the handheld.*
Maybe 'Hello World' is a reference to Cell-to-Cell networking, the process by which Cell-equipped appliances in the home environment would automatically become 'aware' of (and network with) one another, wirelessly or through an online network, without user intervention.
So: Cell-equipped item 'announces' itself to the other Cell products out there = 'Hello World! I'm here! Network with me!'
...or maybe not. Who can say? Still, it's interesting to speculate.
It's for the new eyetoy network in which people can communicate by hand gestures, using the eyetoy. It is also possible to play eyetoy games together with someone from across the globe this way.