By Verne Kopytoff SAN FRANCISCO CHRONICLE Getting telephone directory assistance doesn’t have to cost you a fortune, or at least that’s how many emerging services are pitching themselves. They’re offering consumers free 411, which on its face seems to be an attractive alternative to paying nearly $2, in some cases, for calling a traditional information line. The San Francisco Chronicle recently tested several services to see how they worked. What was found through a combination of landline and mobile phone calls was a wide range in quality. Generally, the services work as follows: You call the number, listen to a short advertisement and then get prompted by an automated voice for a business or residential listing. After listening to a second advertisement, you’re – in theory – told the number you’re seeking or connected to the number directly. Although the services are billed as free, roaming charges and other fees still may apply for mobile phone users. Based on the Chronicle’s test results, I probably would use Google’s service for business and AT&T’s for residential listings for free 411 service.160Want local news?Sign up for the Localist and stay informed Something went wrong. Please try again.subscribeCongratulations! You’re all set! AD Quality Auto 360p 720p 1080p Top articles1/5READ MOREGame Center: Chargers at Kansas City Chiefs, Sunday, 10 a.m.But with the savings come some major trade-offs. Instead of talking to a human, callers must deal with a computer that uses voice recognition technology to field requests. Also count on having to listen to advertisements before getting the telephone number you want. Many companies, including AT&T Corp., have entered the field. Google Inc., the Mountain View search engine, has perhaps the most celebrity, after introducing its version this year and more recently aggressively marketing the service on billboards across the San Francisco area. Although the free directory assistance can be used on landline phones, it is also targeted at mobile phone users, who face some of the steepest charges for traditional directory assistance, and who usually have no access to old-fashioned telephone books while out and about.