Sprint Nextel on Thursday launched a mobile online comparison shopping service powered by startup mShopper that allows people to make purchases by cell phones.

Mobile Shopper is the latest in a string of applications that Sprint, which has been losing ground to rivals, is pushing to try to drive demand for data plans.

But mobile shopping is an uphill battle. According to Forrester Research, U.S. consumers want such mundane benefits as time-savings to adopt data plans. Also, 57 percent of U.S. wireless device owners say they worry about the security of their data when using mobile phones to make payments.

“The issue of the security of the mobile transaction never comes up because the customer pays for the product just as they would online,” Sprint representative Emmy Anderson said. “Mobile Shopper is not involved in the financial settlement. It’s between the customer and the credit card company.”

mShopper is a Boulder, Colorado-based startup whose service compares in-store prices with online prices. Mobile Shopper allows people to check prices at 30 online retailers including eBags, Bluefly, and Shoes.com.

“If users have to take too many steps they will not use it,” said Peter Gorham, an independent wireless analyst. “As it is they will use it only for big-ticket purchases like TV sets. Few are going to comparison shop at the grocery store.”

In March, Sprint introduced a GPS navigation service from TeleNav that it is bundling into its package of data services. The carrier has a number of other services such as mobile TV, NFL Mobile, location-based services targeting parents, and a location-oriented shopping service called Slifter.