As promissed, here's the version of the wallpaper from the season 2 promo for gen 4 iPhone and iPod Touch. It's 640x960 WVGA resolution. Note that it will not work for older iPhones or iPods which had lower resolution displays.

Twilight Sparkle WVGA (960x640)

Twilight Sparkle WVGA (640x960) for gen 4 iPhone / iPod Touch