BEIJING - China Unicom, the country's second largest mobile carrier and official partner of iPhone in China, began Wednesday a new sales contract which bundles iPhone with its subscriber identity module (SIM) card to curb speculative reselling, according to a statement on its website.

If a consumer is found to use the iPhone with another operator's SIM card, the consumer's China Unicom cell number and phone itself will be locked and a penalty will be imposed, according to the statement.

Song Limei, vice president of China Unicom's sales division, said Tuesday that some people bought iPhones from China Unicom and then resold the phones and the cards separately to make a profit.

The company made the new policy to safeguard the interests of both China Unicom and its customers to the largest extent, and offer customers a healthy and orderly market environment, said Song.

Prior to Dec 1, a customer could get an iPhone 4 from China Unicom after paying 5,880 yuan ($880.4) as a deposit and signing a contract to use China Unicom services.

On the second-hand market, the price of the iPhone 4 ranges from 5,600 to 5,800 yuan, and the services, which are worth 5,880 yuan, can be sold for about 800 yuan. The iPhone owner can make a handsome profit in this way.

As China Unicom is the only official partner of iPhone in China, iPhone buyers in China are supposed to use only the China Unicom network. However, other mobile operators are also fighting for iPhone users.

Starting in November, China Mobile began a free service to alter SIM cards so that they can be put into the smaller slot of the iPhone 4.

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Additionally, official websites of some of China Mobile's provincial subsidiaries offer a conspicuous link to "iPhone Zone," which provides detailed instructions to iPhone users using China Mobile services.

On an online posting, many customers said they would not consider buying the iPhone from China Unicom under its new policy because they said it is unfair to users.

However, Song Limei said customers have the right to choose whether they will enter into the iPhone sales contract with China Unicom. Those who want to use other operators' services can choose to buy the iPhone from Apple stores in China.

There are four Apple stores in China at present, two in Beijing and another two in Shanghai.