If these photos of an Asus Transformer 3G is any indication, we might be seeing the 3G variant by next month. We spotted a unit being tested with a Sun SIM card earlier today.
The 3G SIM slot is located on the left side of the tablet, just below the power button and volume rocker. The cradle pops out by pushing into a small pinhole (same as the iPhone).
The only issue now that they’re trying to figure out is a native SMS app which is essential when you load the prepaid SIM or subscribe to a data plan.
They did not suggest any price point for the 3G variant but I guess it will be a couple thousands more than the WiFi-only model.
Disclosure: I bought the Asus Transformer straight from Asus Philippines where they offered dock for free as a special media pre-order discount.