Network operator Telefónica has showcased a linguistic analysis engine that can accurately compile a psychological profile of anyone making a phone call, bringing a whole new meaning to the concept of a mood ring.

The Spanish company, which also owns the O2 network in the UK, was quick to stress that the technology, showcased for the first time to a select audience at this week's Mobile World Congress, would have no commercial application -- in other words it had no intention of using it as a means of selling subscribers to advertisers.

Nevertheless, the technology can construct personality traits with 80 percent accuracy and is designed to monitor voice stress and intonation, rather than record the actual words in a telephone conversation. Telefónica's use scenarios for the concept include being able to recognize when a caller is under duress -- like in a hostage or terrorist situation -- or as a self-analysis tool for its subscribers so that they can map their moods and learn more about themselves in the process, creating an emotional timeline.

Of the technology, a Telefónica spokesman told The Guardian: "This is a proof of concept that our innovation lab has been working on to empower people with their own data to see what it says about them. There are no plans to commercialise this and absolutely no intention of offering this information to advertisers."

However, Telefónica does have plans to offer the technology as an opt-in service to customers in the future and is currently searching for partners to help with its roll out.

The technology, which is yet to be given a snappy name, is in some respects similar to MindMeld, a product from Expect Labs that actively listens to phone conversations in order to complete tasks such as run internet searches, pull up photographs or prompt one of the speakers as to an important diary date.

Some consumers might feel such technologies cross a line in terms of privacy, but the use of personal information is a growing trend with mobile devices. For instance location-based and contextual technologies such as Google Now -- which pushes information to users before they ask for it -- are based on information such as the content of the user's diaries and inbox and their search histories as well as geographical position.