Take this with a "fu√üball"-sized grain of salt, but:
A user on the German apfeltalk forums
recently ordered a refurbished 8GB iPhone 3G. What he got looked like a 3G (standard case, no compass). However, the packaging suggested it actually contained an 8GB version of the
3GS (which is currently only available in 16 and 32GB flavors).
Considering the 3G is already a year 'n' a half old — and Apple's scheduled to unveil a new model next June — it's not out of the question that a low-end 3GS would supplant the 3G. Let's face it, even with less memory, a hundred bucks for a real live iPhone is pretty hard for people to resist.