With no buttons to guide the fingers on its glassy surface, the touch-screen cellphone may seem a particularly daunting challenge. But Mr. Raman said that with the right tweaks, touch-screen phones  many of which already come equipped with GPS technology and a compass  could help blind people navigate the world.

“How much of a leap of faith does it take for you to realize that your phone could say, ‘Walk straight and within 200 feet you’ll get to the intersection of X and Y,’ ” Mr. Raman said. “This is entirely doable.”

ADVOCATES for the blind have long complained that technology companies have done a generally poor job of making their products accessible. The Web, while opening many opportunities for blind people, is still riddled with obstacles. And sophisticated screen-reader software, which turns documents and Web pages into synthesized speech, can cost more than $1,000. Even with a screen reader, many sites are hard to navigate.

Last year, the National Federation of the Blind reached a settlement of a landmark class-action lawsuit against one company whose site advocates found unusable, Target. In the settlement, the retailer agreed to make its Web site accessible to blind people. The federation assesses the usability of Web sites and currently certifies only a handful as being fully accessible.

One challenge is that technology often evolves much faster than the guidelines that ensure Web sites work well with screen readers. In December, the World Wide Web Consortium, an Internet standards group, released Version 2.0 of its accessibility guidelines for Web sites. The previous version dated back to 1999, when the Web consisted largely of static Web pages rather than interactive applications.

Obstacles on the Web take many forms. A common one is the Captcha, a security feature consisting of a string of distorted letters and numbers that users are supposed to read and retype before they register for a new service or send e-mail. Few Web sites offer audio Captchas.

Some pages are just poorly designed, like e-commerce sites where the “checkout” button is an image that isn’t labeled so screen readers can find it.