For years, Melissa Reiter has been trying in vain to drop 10 pounds. She works out regularly, lifts weights and practices yoga. Now she has found a new activity that she hopes will boost her chances of success: working her mobile phone.

Two weeks ago, she signed up for Nutrax, a free online diet service that lets her use a camera phone to snap pictures of her meals, send them to an online account, and receive a summary of her meal's calorie intake, its carbohydrate, fat, and nutritional content, and her progress toward her diet goals. "The helpful thing is that you can immediately see the results of the decisions you make," says Ms. Reiter, a 37-year-old accountant in Chicago.

Increasingly, diet and nutrition services are going mobile, as they team up with cellphone carriers and digital-device makers to provide instant, on-the-go diet information and assistance. Their offerings vary from tools such as carb and calorie counters to personal advice from dietitians. The services, now offered by U.S. cellphone carriers including Cingular Wireless, Verizon Wireless and Sprint Nextel Corp., incorporate some of the most popular diet plans, including those from Atkins Nutritionals Inc., Weight Watchers International Inc. and the South Beach Diet. At the same time, a growing number of diet companies offer software and services that can be accessed by any cellphone or personal digital assistant.

But as with most diet trends, it remains to be seen whether the diet-to-go concept will represent much of a leap forward for dieters. Most cellphone and diet companies won't say how many people are using such services. Dietitians say cellular diet applications have the potential to work, but there are some limitations: Sending a snapshot of a meal over the phone to a nutritionist, for instance, doesn't provide precise information on serving size, ingredients (butter? olive oil?) or method of preparation.

"It's good for keeping on track, getting feedback, but not necessarily for getting a healthy diet," says Christine Gerbstadt, a spokeswoman for the American Dietetic Association, which represents food and nutrition professionals. She adds that such programs aren't a substitute for the personal guidance of a diet counselor, and users of diet applications on cellphones should have basic knowledge of what they are doing before they start out.

For cellphone companies, incorporating diet applications into their devices is part of a strategy to attract more customers by offering multipurpose devices that go far beyond making phone calls. For dietitians and nutritionists, making these diet plans available on cellphones and other devices means larger sales of their products.

Some of the latest products give users a general picture of their health. Nokia Research Centre, a division of Nokia Corp., is working with VTT Technical Research Centre of Finland and the University of Tampere to launch WellnessDiary, a free fitness-software application for its S60 smartphones, next month. When users enter their weight and other health-related variables such as diet details, they will be able to get on-screen feedback, including graphs showing their weight history. The S60 phones such as the Nokia N91 are sold in the U.S.

But most companies focus on helping dieters crunch food and nutrition data on the spot, a process that has long been cumbersome. In May, Sprint Nextel and Quebec-based MyFoodPhone Nutrition Inc. launched a service called MyFoodPhone, which enables users to snap pictures of their meals and send them to a nutritional adviser for review. In return, they get one-minute diet and nutrition video clips, some of which are personalized to address eating habits, sent biweekly to their devices. The service costs $9.99 a month.

Cingular, in conjunction with diet-software provider Digital Chocolate Inc. of San Mateo, Calif., provides Atkins2Go, a weight-management application, on 21 devices. The software, which costs $9.99 to download, allows users to find out the carbohydrate counts of various foods, log the portions eaten along with the carb counts and track weight loss over time. Cingular is a joint venture of AT&T Inc. and BellSouth Corp.

Meanwhile, Verizon Wireless, a joint venture of Verizon Communications Inc. and Vodafone Group PLC, is providing through its Get It Now service two diet services, the SkynetMD Diet Fitness Diary and the Diet TinyAssist applications. Both services are meant to provide Verizon cellular users with calorie, fat and protein counters, as well as other information. The Diet Fitness Diary costs $1.99 a month and the Diet TinyAssist application, which offers more-personalized diet tools, costs $2.99 a month.

Deutsche Telekom AG's T-Mobile USA doesn't offer its own diet service, but users can access Web-based services over its devices.

The mobile movement extends beyond cellphone carriers. Palm Inc. introduced four applications last year: Atkins Carb Counter, Keyoe Diet & Exercise Assistant V6.0, Weight Watchers' On-the-Go and the South Beach Diet OnHand, a software version of the South Beach Diet for Palm devices and PDAs running Palm OS 3.5 or higher.

There are a growing number of services not affiliated with major companies to choose from as well. All the services can be accessed by cellphone or PDA via the Web. Software maker Handango Inc., based in Hurst, Texas, sells diet applications designed for cellphones and PDAs online that users can download from its Web site, handango.com, onto their phones. The company provides a number of applications, including Diet & Exercise Assistant, which manages users' daily nutrition, exercise and health, and MyPersonalDiet, which helps users look after their weight by defining and tracking their diet and nutrients.

Meanwhile, Boston-based Nutrax Inc., the diet-consulting service Ms. Reiter uses, bypasses the carriers altogether. Users of any Web-enabled cellphone or PDA can sign up on its Web site, nutrax.com, to create accounts, take pictures of their food and send them in to their accounts for analysis. The service can be used for free, or users can register for $8.95 a week, which includes advice from a professional dietitian. According to Thomas Batten, co-founder of Nutrax, nearly 5,000 users so far have used the company's diet software.

Other cellphone diet aids include downloadable applications from Web sites like dietorganizer.com, which works on cellphones, BlackBerrys and PDAs. Users pay a one-time fee for downloading the software.

Integrating diet and health-related services into cellphones and PDAs is taking off in other parts of the world as well. In the United Kingdom, for example, Nutratech Ltd., a weight-management service that started online, launched a stand-alone mobile version in January. And a British phone service called Hutchison 3G UK Ltd. brought Atkins2Go to cellphones last year. In Japan, there are 12 diet-related services available on NTT DoCoMo Inc.'s i-mode, one of Japan's most popular phone systems.

Ms. Reiter of Chicago says she opted for the Nutrax service instead of a clinical dietitian because it is free and immediate. And while a dietitian might ask her to keep a food journal, she thinks taking pictures will create a better account of her diet. "It's fine to have a half-cup of ice cream, but it's a different story if you're having the entire pint," she says. "Just writing down in your food journal that you had ice cream really doesn't tell the whole story."