The mobile phone is quickly becoming Santa’s biggest helper.

Powerful software applications for devices like the Apple iPhone are making it easy for bargain-hunting consumers to see if another retailer is offering a better deal on a big-screen HDTV or pair of shoes and to use it to haggle at the cash register.

Online retailers are revamping the mobile versions of their sites so consumers can make purchases without tedious typing. And offline retailers, battling for every last dollar, are sending cellphone users electronic coupons to lure them away from competitors.

One in five shoppers said they intended to use their cellphones to shop this holiday season, according to an annual survey by Deloitte, the accounting and consulting firm. Of those, 45 percent said they would use their phone to research prices, 32 percent said they would use it to find coupons or read reviews and 25 percent said they would make purchases from their phones.

Of course, mobile shopping technology is still somewhat clunky, between erratic Internet connections, outdated pricing data and balky product scanners.

But smarter phones and a heightened bargain-consciousness among consumers are spurring a level of innovation in e-commerce last seen during the height of the dot-com boom a decade ago.

In addition to ShopSavvy, mobile apps from RedLaser, TheFind, ShopStyle and PriceGrabber.com allow customers to compare prices across a range of retailers. Retrevo, an electronics review site, has a service called RetrevoQ that lets users send a text or Twitter message with the name of the product they are considering and get an immediate response with a recommendation of whether to buy it and a range of online prices.

While searching for prices is easy, buying from the screen of a cellphone is more difficult. It generally involves clicking to the retailer’s Web site, which is often not customized for a mobile phone’s tiny screen, and then entering shipping and billing information using the tiny keyboard.

To fix that, some retailers are building sites and applications specifically for cellphones. The iPhone app for the Tommy Hilfiger online store, for instance, shows select products based on what shoppers are looking for so they do not have to scroll through pages of clothes. Those who are registered on the Web site need only enter their e-mail address and password to check out.

“Retailers need to realize that if you give people a way to make it easy, people will shop on their phones,” said Kelly O’Neill, product marketing director for ATG, which provides e-commerce technology to retailers and built Tommy Hilfiger’s app.

EBay’s iPhone app sends people notifications if they are outbid in an auction and lets people check out with just a few clicks if they have a PayPal account. Mobile shoppers will spend $500 million on eBay this year, the company said.

By improving ease of use, savvy online retailers are snatching sales from bricks-and-mortar ones. Matthew Tractenberg, for example, was recently shopping in a Silicon Valley bookstore, where he picked out five books for a total of $80. Before taking them to the counter, he typed the titles into the Amazon app on his BlackBerry Curve. Amazon had the books for $50 and would not charge sales tax or shipping. He placed the order on the spot and left his small pile of books in the store.

“It’s almost easier than doing it on a computer,” Tractenberg said. (NYT)