Instant messaging over mobile phones emerged as a key topic at the 3GSM World Congress in Barcelona, with three major announcements made within a 24-hour period beginning Monday.Each announcement represented a key link in the mobile IM value chain: mobile phone operators, Internet telephony companies and software makers.If you're wondering, however, why the GSM Association (GSMA), representing the interests of GSM mobile phone operators, Skype and Microsoft didn't make a joint statement, the answer is - for the most part - competition."Instant messaging and presence services are very attractive features to add to mobile phones," said Saul Klein, vice president of marketing at Skype. "We're going to see different players competing in this market."Microsoft hopes to make its Microsoft Office Communicator Mobile software, offering IM functionality, a ubiquitous feature of mobile phones.On Tuesday, CEO Steve Ballmer showed the soon-to-be-released software running on a smart phone and linked over the air to a computer running Microsoft Office Live Communications Server. Using the software's presence notification function to find a colleague online, Ballmer placed a VoIP call to that person from the smart phone.An hour later, Skype CEO and co-founder Niklas Zennstr\u00f6m made two announcements, each targeting the IM market. The company will extend its PC-based VoIP service to mobile phones, naming the Hutchison 3 Group (Hutchison 3G) as its first mobile phone partner, and has launched Skype for Pocket PC 2.0 for portable devices running Windows Mobile.The day before, several of the world's largest mobile phone operators announced plans to offer IM service across their networks as part of a GSMA-driven initiative to make IM service globally available and interoperable. Unlike the free IM service available on fixed-line networks, however, the service planned by the GSM community will cost money, with the calling party picking up the tab.The operators, including Vodafone, Orange, Telef\u00f3nica M\u00f3viles and T-Mobile, were mum on how exactly they plan to offer IM service. But the fact that they intend to make money from IM suggests they are likely to offer the service through their own mobile portals, such as Vodafone's Live.Asked if interoperability is an issue with rolling out a mobile IM service as mobile operators claim it is, Klein said Skype software is device and network agnostic. "I don't see where we will have any major interoperability problems," he said.We'll know more in a few months.