Several of the world's largest mobile phone operators have agreed to offer instant messaging across their networks as part of an initiative to make IM service globally available and interoperable.Fifteen operators, including China Mobile Communications, Vodafone Group, Orange, Telef\u00f3nica M\u00f3viles and T-Mobile International, have joined forces to help kick-start the mobile phone IM initiative, which is being spearheaded by the GSM Association (GSMA), the group said Monday at a news conference during the 3GSM World Congress in Barcelona.The group also hopes to cooperate with Internet-based IM service providers, such as Microsoft's MSN, America Online and Yahoo, according to Vodafone CEO Arun Sarin. "We want to extend this service and make it a bigger experience for users," he said.Microsoft, Yahoo and AOL already provide wireless access to their IM services but this initiative's goal is to extend the availability and interoperability of wireless IM globally. MSN Messenger, Yahoo Messenger and AOL AIM don't interoperate, although Yahoo and Microsoft are working to build links between their services.In the first phase, the mobile operators aim to extend IM -- a widely popular service among PC users in the fixed-line telecommunications market -- to their combined customer base of 700 million users. Over the coming months, they expect other GSM operators to join the initiative, representing a potential global market of more than 2.2 billion people.On the Internet, more than 300 million people around the world use IM, and around 12 billion messages are sent every day, according to GSMA.Unlike the free IM service available on fixed-line networks, however, the IM service planned by the GSM community will cost money, with the calling party picking up the tab.Vodafone views IM as an opportunity to "add value" and create a new revenue stream, Sarin said.The CEOs of six network operators attending the news conference declined to discuss pricing details.A key requirement for providing an IM service to mobile phone users is interoperability to ensure that messages can be sent across networks around the world, said Sanjiv Ahuja, CEO of Orange. Operators within the GSM community have agreed to IM interoperability standards, he said.Most high-end smart phones and many low-end phones are already IM-enabled, according to Orange's Ahuja. He expects IM to become a standard feature of GSM phones moving ahead.The operators expect to begin rolling out IM services over the next several months.