What is jd4iphone?

It's a Japanese version of iPhone, and there is no serial number starting with J in China.

The first letter "C" of the serial number of Apple iPhone stands for Shenzhen, "D" stands for Chengdu and "F" stands for Zhengzhou. Look at the last two digits of the serial number version of Apple's mobile phone. The last two are CH of China Bank, ZP of Hong Kong Bank, KH of Korea, LL of America, DN of Germany, ZA of Singapore and Malaysia, AB of UAE, RS of Russia, GR of Greece, IP of Italy, PP of Philippines and FB of France.