Dang! Missed this 3GS case completely.

[mcdj]

From some random Chinese site. Would love to see a slider like this for the 4, though it also makes me miss the curved back.

 

[Bawstun]

Would've loved that case in place of my InCase Slider when I had my 3GS. I never knew about it either. Available in other sweet colors I bet too.

Damnit, lol. Maybe they'll iP4 clone it.

 

[Pared]

http://chinaontrade.com/iphone-3g-3gs-accessories-back-cover-marble-series-c-69_81.html

These are MUCH nicer colors than the Incase slider.