The pickpocket is believed to have taken the Apple handset from Zou Bin when they shared a taxi, the Xinhua news agency said.
Zou had nearly 1,000 contact numbers in the device and with no backup copy -- like millions of other people around the world -- he was more concerned about losing the data than the phone itself, it added.
"I know you are the man who sat beside me. I can assure you that I will find you," he said in a text message to the thief.
"Look through the contact numbers in my mobile and you will know what trade I am in," he added. "Send me back the phone to the address below if you are sensible."
The tone of the message was unmistakably threatening – Zou works in the pub industry, which in China is widely held to have links with gangs.
Days later he received a parcel containing his SIM card and 11 pages of carefully handwritten contact numbers, Xinhua said, adding he was "fossilised" by the result -- a Chinese colloquialism for astonished.
"It would take a while to write from one to one thousand, let alone names and a whole string of digits. I suppose (the thief's) hand is swelling," Zou was quoted as saying.
The theft earlier this month is believed to have happened somewhere between Yiyang and Changsha in the central province of Hunan.
Chinese Internet users gave the thief plaudits for his efforts, dubbing him "the conscience of the (theft) industry".
One user of Sina Weibo, a Chinese equivalent of Twitter, posted: "What a sympathetic and faithful thief, one who values professional ethics."