In a Sunday press release, Apple announced an on-sale date for the iPhone 4 in China. Saturday, September 25, 8 am is when customers in the world's largest market can get their hands on the new phones; both the Apple Store Hong Kong Plaza in Shanghai and the Apple Store Xidan Joy City in Beijing will be carrying them, coinciding with the opening of the Bejing store.
China Unicom (the phone's domestic carrier) will also be selling them in retail stores. Just as in other countries, new purchases via China Unicom will require a two year service contract; however, the phone will also be available contract-free at the Apple stores.
Suggested retail price for the phone is CNY4,999 (around $744) for the 16GB model and 5,999 yen (about $893) for the 32GB model (contract-free pricing; China Unicom pricing includes service plan prepayments, and it's available here). China Unicom has been accepting pre-orders for a few days now.
[hat tip to @Khaled]