Originally posted by Rainecloud
There's nothing on the actual box of the game to tell you that the version is PAL or NTSC, which is why the game is working on your American GBA SP. Therefore, I'd also presume that you will have no problem when it comes to you linking with your friend's copy. I've only ever heard of problems arising when people have tried to copy data from Japanese to American versions of the game whilst using an 'Import' piece of software. Considering that the game is already working perfectly on your machine, I can't see any problems.
I felt the urge to correct a few things. xD
- There's no such thing as PAL or NTSC on a BG/GBC/GBA/SP.
- The explanation why a GB(/C/A) game works on any GB(/C/A) is because there's no region code.
- NTSC/PAL isn't why other console games don't work from one country to the other, it's the region encoding; Japan and USA have the same TV standard (NTSC), but you still can't play imported J games without using a trick (chip, disk swap, bootloader...).
- Linking might not work because some parts of the game have been modified (5 languages instead of one), and it may also involve what is transmitted through the link.
- Data import probles come from the previous point, and on the GC, from another: the memory card format. There are two ways to format a GC memcard, and there not compatible (so if I were to save from a US/J version of WW on my card containing EU formatted data from MKD, I'd lose that data because my card would be reformatted).