Here’s what’s coming out of Taiwan. Asustek, BenQ, and a few other lesser-known brands are currently "developing iPhone -like products" and that the first out of the gate will likely be something from Asustek that’ll be available "as soon as the first half of 2008." The devices will run Windows Mobile and be marketed to business users with GPS and 3G features, so actually not really similar to the iPhone at all.
I learned my lesson about launch dates this summer, so I’ll assume that "first half of 2008" means the last possible day that qualifies as a day in the first half of the year. So roughly a year after the iPhone launched, there will be similar devices on the market. Can’t wait!