Microsoft Corp. and Orange SA will link their instant messaging systems later this year, allowing up to 375 million people to chat with each other using their PC or mobile phone, the companies said Wednesday. In reality, take-up will be much more limited.

Orange will offer its French mobile phone and Internet access customers a new service in December called Orange Messenger by Windows Live. It will extend the service to the U.K. and Spain next year, making it accessible to 135 million Orange customers in total, the company said Wednesday. Microsoft puts the number of Windows Live Messenger customers at 240 million.

Behind those numbers, though, the immediate potential of the link-up is more modest. Just 700,000 of Orange’s customers will have handsets compatible with the service when it launches in December, said Didier Lombard, chief executive officer (CEO) of Orange’s parent company, France T