America Online says it will try to block Tribal Voice's upcoming version of its PowWow instant messaging service from connecting with its own Instant Messenger technology -- just as it has gone to war with Microsoft. Tribal Voice plans to offer the new service in the fourth quarter, and will include it in the co-branded messaging software it currently provides for AT&T's WorldNet and is developing for UK-based Freeserve. Tribal Voice said it will use protocols AOL had published earlier this year to let developers of Unix-based applications access its service. But in the wake of a very public battle with Microsoft over instant messaging, AOL has since removed links to those protocols from its Web site. The furore arose after Microsoft released its MSN Messenger program, which included a workaround that allowed users of Microsoft's program to communicate with AIM users. AOL repeatedly has tweaked its software to block Microsoft, while Microsoft has attempted to counter each changes. As of the last week or so, AOL has been successfully blocking Microsoft communications. Microsoft has said that it is not using the contested protocols to access AOL's servers. Tribal Voice said Tuesday that it hasn't received explicit permission from AOL to tap into its AIM service. Instead, the company characterized the new feature as "uncooperative interoperability". While AOL has removed the links to its protocols, it has left access to its messaging server open to open-source developers. "I believe that in order for AOL to lock us out, they would effectively have to block anyone who's built an application that uses their virtual phone line," said Richard Dym, vice president marketing for Tribal Voice. An AOL spokeswoman said Tuesday that AOL never intended the protocols to be used by competing companies. "It was designed to allow people to use QuickBuddy, a thin version of AIM (that enables) instant messaging within Web pages. It was never designed or posted with the intention of allowing companies to run their instant messaging on our servers," she said. The spokeswoman said AOL, which has signed deals with other ISPs to offer branded instant messaging, hasn't signed any such deal with Tribal Voice. "Anyone who's going to try and gain unauthorised access to our servers will be blocked, because we want to protect the privacy and security of our users," she said. While AOL dominates the instant messaging market with more than 80 million subscribers to AIM and its ICQ service, competition has been growing. Microsoft claims that two million people have subscribed to MSN Messenger. Tribal Voice said it has five million subscribers for its PowWow service. Adding WorldNet and Freeserve users will up that number to around eight million, Dym said. The move will also give Freeserve, the largest ISP in the UK, another weapon to combat AOL, which recently launched its own free service there.