Supplies of Apple's latest iPhone 4 have run out on the California-based company's new online China store and at some brick-and-mortar outlets across China.

China Mobile is offering to help consumers convert their standard-sized SIM cards to micro-SIM cards for use in iPhone 4s. The move is part of an effort by the nation's largest mobile carrier to appeal to users of the Apple device.

"China Mobile is planning to win back users it has lost since late last year when China Unicom was named the authorized distributor of the iPhone in China," said Ji Chendong, a technology consultant with consulting firm Frost & Sullivan.

China Mobile recently began offering the conversion service free of charge. It allows existing subscribers' SIM cards to fit in the popular new Apple phones.

Supplies of Apple's latest iPhone have run out on the California-based company's new online China store and at some brick-and-mortar outlets across the country.

Conventional SIM cards don't fit in the card slot of the iPhone 4 unless the edges are trimmed. While phone users can snip the cards themselves, they can easily be rendered unusable. China Mobile outlets in Beijing and Shenzhen offer the free service, while Shanghai stores sell the micro cards.

Savvy sellers are also offering the card-cutting service on Taobao.com for around 10 yuan ($1.50). Do-it-yourself cutting devices can be found on the site for around 30 yuan ($4.49).

The iPhone grabbed about 6 percent of the nation's smart phone market by the end of the third quarter this year, in contrast with a 2 percent share a year ago, according to consulting firm Frost & Sullivan.