Service provider revenues are under attack from all quarters, and 411 directory assistance can be added to the list. Both Google and Microsoft have rolled out free 411 services, or at least free until they eventually add locally targeted voice-based advertising to the mix.

Google made its offering available as a Google Labs project last week. Microsoft announced its offering Oct. 15 as part of a large update of its search offerings, although its voice 411 service isn't live yet.

The new Google Voice Local Search is basically 411 service delivered for free. Customers dial 800-GOOG-411 and interact with a voice recognition system. The service is currently focused on helping customers find businesses, either by name or description. Once a caller finds the desired business, Google will connect the customer for free or send a text message with details.

Because the service is still in Google Labs, it doesn't include advertising. But it fits into Google's long-term vision of extending its ad reach as broadly as possible, including to services that tread on traditional telco business.

Microsoft, meanwhile, announced Live Search 411. Jointly developed with Tellme Networks, acquired by Microsoft earlier this year, the service is available via 800-CALL-411. Like Google's offering, customers call the number, track down a business, and can either be connected at no charge or receive a text message in return.

Google and Microsoft aren't the first companies to roll out free 411 services, though their size and scope automatically make them forces to be reckoned with.

Start-up 800-FREE-411 offers a similar service and already has targeted advertising built in to help fund it. The service also covers residential and government listings, and offers a live operator backup in case the voice recognition system can't deliver a match. Meanwhile, TellMe offers a beta version of its service live today at http://beta.tellme.com.

HOW FREE 411 SERVICES WORK

1. Dial an 800 number.
2. Ask for a business listing, or narrow down from a category search
3. The call is connected for free, as the caller hears a related audio ad.
4. Optionally, the listing information can be sent as a text message.