China Unicom is now accepting pre-orders for the iPhone 4. According to a Wall Street Journal report, the handset is priced between 5,880 yuan to 6,999 yuan (roughly $874 to $1,040), in line with what the carrier charged for the iPhone 3GS when it launched in China last October. The report states that sales have picked up after a slow start, but are still hampered by China Unicom’s exclusivity. Citing a surveys of young Chinese mobile subscribers…