GT4
only exists so far in NTSC Japan version.
The NTSC US and PAL European version will be released whenever PD decides so. (I'll believe it's in May when I actually get my copy from the retailer
).
If you really can't wait you can buy GT4
on ebay, but you also need to buy the JP PS2 to use it.
Only 2 questions remain :
1) how impatient are you ?
2) how rich are you ?
For myself, I'm much more impatient than rich, so I'll wait for the PAL version.
BTW, Sony released a limited version japanese white PS2, with white controller and it was sold in bundle with GT4
.
(Just in case you're extremely rich
)