The trumpeters sound great when they blare out those old Communist marches, but $16.99 plus tax seems a bit steep for a greatest hits CD from the Soviet Army Chorus and Band.

I discreetly grab my cellphone, dial a toll-free number and wait for the robotic voice to ask my ZIP code.

I then use my number pad to key in the CD's bar code.

Three seconds later, the voice tells me that Amazon offers the same CD for $12 – shipping included. I raise my finger to press one extra button and place the order.

Price comparison tools have long enabled consumers to bargain-hunt from home computers, but new mobile services make it easier for in-store shoppers to save via cellphone.

Sadly, all tested services still suffer major shortcomings.

Keyword-based services such as Google's Froogle often return irrelevant listings. The top results for "Price Dell Latitude Laptop" are AC adapters, not computers.

Barcode-based services such as Frucall Inc. always return the right product – except when they don't return anything, which is often. Enter the barcode from a wine bottle or a cocktail dress, and they'll probably fail.

Such caveats aside, these services can save shoppers a bundle under the right conditions.

A local Barnes & Noble sells a recorded version of the David Sedaris book Me Talk Pretty One Day for $29.98 plus tax. Search services found it for $8.44 at Alibris.

Of the five tested services, I found Frucall's three-step system easiest to use.

First, dial 1-888-363-7822.

Second, enter your ZIP code so the system can estimate shipping.

Third, enter the barcode. The system returns prices almost instantly.

Frucall doesn't require Internet-enabled phones or user accounts, but users who create accounts can place orders over the phone.

A text-based service called Mobsaver is nearly as easy to use.

Shoppers can text a product barcode to save@mobsaver .com and get comparison prices from Amazon and eBay.

Like Frucall, Mobsaver does not require accounts but will save search results for account holders.

The company offers no purchase options, though, and with only two Web sites for comparisons, it can miss good deals.

ScanBuy Shopper, on the other hand, casts a massive net. It scours Amazon Marketplace, PriceGrabber, Shopping.com and Yahoo Shopping for prices, and it finds some real steals.

Unfortunately, ScanBuy won't work on many cellphones, won't estimate shipping charges and won't support instant purchases.

ScanBuy can theoretically let shoppers compare costs for nearly any product that's sold online.

In practice, the system works best when customers can handle original packaging with manufacturer barcodes. Retail price tags generally feature in-house barcodes to prevent price comparison.

The price tags at Macy's and Dillard's, for example, tricked all the barcode-based systems, even for national brands that sell online.

Text search should conquer deceptive barcodes, but I found only one phone-friendly text service, Froogle, and it bombed.

Google has pared down its search services for text messaging. Users simply text a few key words to 46645, and Google returns results. Users tap Froogle by starting queries with "price" as in "price Dell Latitude."

It takes only seconds, but results dissappoint. After suggesting adapters rather than computers, Froogle confused a search for a 2006 book called The Immortal Game.

The system returned prices for a 1999 book with the same title.

I ended my quest for mobile bargains by visiting standard price comparison sites such as PriceGrabber and Pronto on my phone's browser.

The results bested Froogle, but each search took an eternity even on a good mobile network, and sheer information transfer would bankrupt anyone who lacks an unlimited data plan.

Bottom line: Mobile price comparison systems leave much to be desired, but I'd still recommend Frucall and ScanBuy (if your phone supports it).

Under the right circumstances, both of these free services can answer a question that has plagued shoppers for a decade now: "I wonder if I could get this cheaper online?"