(101122) -- HAIKOU, Nov. 22, 2010 (Xinhua) -- The picture taken on Nov. 22, 2010 shows an indoor poster about mobile number portability at a China Unicom service center in Haikou, capital of south China's Hainan Province. The commercial trial of mobile number portability was launched Monday in Hainan Province as well as north China's Tianjin Municipality. In the six-month-long trial, mobile subscribers in Tianjin can change their carriers while retaining their original numbers. In Hainan, only China Mobile users are allowed to switch to other networks without chaning phone numbers. There are three mobile operators in China, namely China Mobile, China Telecom and China Unicom. (Xinhua/Guo Cheng) (ljh)