After selling only 5,000 iPhones in the handset’s first five days on sale, China Unicom has revealed (Translated Link) that it has now sold more than 300,000 iPhones in mainland China. A China Unicom GM told the press December 27 that the company would hit the 300,000 sales mark either later that day or on the 28. The announcement comes just 20 days after the company announced it had reached the 100,000 unit plateau; by comparison, it took the…