Google is testing a service that will make transcripts of voice-mail messages and make them searchable.

At the moment, Google is only offering transcriptions to existing customers of GrandCentral Communications, a telecommunications service provider that it bought in July 2007, it said in a posting on the Official Google Blog.

GrandCentral offers customers a single number through which they can forward calls to their work, home or mobile phone, filter calls before answering them, record conversations and access an archive of recordings and voice mail via the web. Just like Google's promise that with its Gmail email service, you'll never need to delete another message, GrandCentral promises to archive voicemail "for life."

Google isn't saying yet whether it will make and store transcripts of recorded conversations in addition to voice-mail messages.

GrandCentral stopped accepting new customers after Google bought it and even now, rebranded as Google Voice, the service is still closed to new business. Since its acquisition, GrandCentral has invited prospective customers to leave their email address to reserve a number, and Google said it will begin responding to those requests "in a matter of weeks."

Google claimed its service was the only fully automated voice-mail transcription service on the market. The transcriptions may include mistakes, and Google will make accuracy improvements over time, it said.

In contrast, other automated transcription services already on the market rely on a small amount of human intervention to improve transcription accuracy and teach the software new words on the fly.

Last week Skype began transcribing its customers' voice mail messages into SMS text messages using technology from British company Spinvox. If the Spinvox software is unsure about a word, it plays that part of the recording to a person who confirms or corrects the transcription.

Spinvox began launching services in the U.K. in 2005 and now powers the voice-mail transcription services offered by North American carriers including Alltel, Cincinnati Bell, Rogers and Telus. Telus will send transcripts to its subscribers via SMS or email.

Another software company, Nuance Communications, announced a competing offering last April. It hasn't named any customers yet, but operators in France and Spain are deploying its voice mail-to-text service, a company spokesman said last month.

Skype makes its transcription service pay for itself by charging for the SMS messages, but Google hasn't said how it will make money from its transcriptions, which like other GrandCentral services are free.

One obvious revenue source for Google would be targeting advertising: when a friend leaves a message suggesting you meet for dinner, the transcript might be displayed alongside an advertisement for a local restaurant. Google might also use the transcripts to improve the profiles of its users' interests that it is building in order to deliver interest-based or behavioural advertising, a move it announced on Wednesday.