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(CNN) -- Mobile phones can be used as cameras, radios, MP3 players and personal organizers -- and now, they can also be used as walkie-talkies.
Already popular in the U.S., particularly with teenagers, Push to Talk (PTT) services are making their way into Europe.
PTT works a bit like a walkie-talkie, allowing instant conversations with selected people at the push of a button.
Mobile phone company Orange is the first service provider to offer PTT systems in Europe, launching "Talk Now" in France and the United Kingdom late last year.
Orange spokesperson Jenny Thorpe told CNN the service was available only to corporate clients at present, and was offered only on one type of handset, the Handspring Treo 600.
She said that while PTT services were popular in the teen market in the U.S., Orange believed the service would be useful in business, for tradesmen and corporate management.
The service works like this. The telephone in question has a special PTT button on the side, which when pushed, connects the user to 10 people on a buddy list.
The buddy list works in a similar way to buddy lists on computer instant messaging systems, displaying who is available for a chat and who is not.
No telephone number is dialed and the connection is immediate -- as long as users hold down the button while speaking, they will be heard by everyone who is available on their buddy list.
If the conversation turns lengthy, participants can switch to a conference call, Thorpe said.
Talk Now works anywhere there is Orange coverage. It uses technology that runs on top of the Orange GSM-based network, using traditional circuit-switched technology.
In the U.S., PTT is operated using packet switching, where voice data from the caller is split into packets, sent and then reassembled at the recipient's end.
And while the idea might be new in Europe, American researchers are already working on a way to make PTT even more high-tech.
Dr Paul Aoki, from the Palo Alto Research Center (PARC) in California, is one of a group of scientists who is working on software that will be able to read the level of interest of the voices of those involved in PTT conversations.
The work was presented at the International Conference on Spoken Language Processing (ICSLP) held in Korea in October and is part of a large project currently being undertaken on mobile audio communication.
Aoki told CNN that the technology would be used to automatically switch people from PTT systems to more private means, such as a conventional telephone call.
It would do this by examining the level of interest in the participants' voices, including tone of voice and prosodic style, which includes changes in strength, pitch and rhythm, all of which contribute to detecting the ebb and flow of conversations.
Aoki said although PTT systems were easy-to-use, being able to ask for more privacy could sometimes be difficult.
"It's often difficult socially to be switching back and forth. It's difficult to say, 'let's switch to a phone call.'"
He said that if a computer was able to understand human feelings by analyzing a variety of different aspects of human speech, it opened the way for several different new functions, including bridging the social problem of asking for more privacy.
The technology would monitor participants' conversational engagement -- whether they were actively involved in a conversation -- and automatically switch those whose level was high, to a private conversation.
If they became disengaged, the technology would switch them back to the more public domain, he said.