Yahoo and MSN Messenger instant messaging users will have to wait a bit longer for the promised interoperability between the two services.

Yahoo and Microsoft said late last year that they would launch a service in the second quarter of this year that would allow their customers to send and receive messages and share buddy lists between the two instant messaging (IM) networks. With the second quarter come and gone, representatives from both companies say the interoperable service will launch globally "very soon."

When the service does launch, it's unlikely to include any additional capabilities than those that were announced late last year. At the time, the companies said the service would let users exchange messages, see buddy online presence status, share some emoticons and add buddies from either service to their lists. But they didn't say that the service would support some widely-used features such as voice, photo sharing or video conferencing.

"We will continue to jointly innovate and explore the delivery of enhanced services to users, including voice, which we believe is an important component of IM interoperability," Microsoft said through its public relations company The Red Consultancy. There are technical issues that the companies will have to address to support voice interoperability, the company said.

MSN Messenger is likely to interoperate with other IM networks in the future, the company said. "We need to assure that the costs of interoperation are in line with the business benefits," it said.

Yahoo, however, doesn't have plans and doesn't expect to interoperate with other IM clients, said Nicola Jones, a Yahoo spokeswoman.

IM users have long clamored for interoperability between clients but IM service providers resisted as they competed against each other to build the largest customer base.

The threat of competition from Google's IM service, launched in the middle of last year, may have driven Yahoo and Microsoft to team up in hope of combining their weight against the new entrant.

The battle lines are clearly drawn. At the end of last year, Google and AOL said they'd make their IM services interoperable.

The two camps, with Google and AOL on one side and Yahoo and Microsoft on the other, even support competing protocols that enable the interoperability. Google supports the XMPP (Extensible Messaging and Presence Protocol) protocol while Microsoft and Yahoo will connect their IM offerings using SIMPLE (Session Initiation Protocol for Instant Messaging and Presence Leveraging Extensions). SIMPLE and XMPP are competing protocols, both part of standards-making processes in the Internet Engineering Task Force standards body.

The battle between the groups may also be affecting third party companies. Cerulean Studios offers the popular Trillian IM client software that allows users to combine many IM services within a single user interface. The software was part of Google Pack, a collection of free software that Google promotes, but was abruptly dumped from the suite in May. Google didn't explain the reason for deciding not to include Trillian in the Google Pack.