Apple Inc's locked iPhone 4, though not yet available on the Chinese mainland, has risen in price by 20 percent in the gray market, Shanghai Daily learned Wednesday.

Price of a locked iPhone 4 16GB smuggled from the United States, which doesn't even support phone calls, jumped 20 percent to 6,500 yuan (US$955) in the gray market after hints that it soon may be unlocked easily. The unlocked iPhone 4 16GB, from the United Kingdom and Hong Kong, dropped by half to about 8,200 yuan.

The iPhone 4's debut in Hong Kong on July 30 depressed the price of unlocked iPhone 4s in the gray market.

In the US, Apple locks iPhone 4 with AT&T's mobile services. It means that people can't use it with their subscription to other carriers, like China Mobile.

"Few sellers are willing to sell the US version of iPhone in the (gray) market now. So you have to pay more," said a distributor surnamed Yang, who has sold smuggled iPhones since 2007.

The US version of iPhone 4 will be unlocked within a month, Yang added.

The iPhone 4, the fourth generation and successor to iPhone 3GS, features video calling, e-books and a stainless steel frame that acts as an antenna.

It debuted in the US market in June and in Hong Kong on July 30. There is no timetable for its release on China's mainland and it's notably absent from Shanghai's Apple Store which opened last month.

Most Chinese consumers buy gray iPhone 4s for up to double the overseas retail price of HK$4,988 (US$639) for each 16GB model.

At present, users can buy the gray US version iPhone 4 but it's nothing but a "brick," because buyers can't make calls or send messages.

An overseas organization, called iPhone Dev Team, announced at the weekend it would soon release tools to unlock the phone.

"It's worth waiting for. It's a professional team and it has never broken promises before," said Pang Xiumin, a handset product editor for the IT website PCHome.

The price of the US version jumped from 5,300 yuan on July 30 to about 6,500 yuan yesterday. The price of unlocked iPhone 4s from Britain or Hong Kong dropped from 12,000 yuan to about 8,000 yuan, according to a distributor surnamed Sun.