Nokia is previewing its upcoming Messaging/IM hybrid application by releasing a Java-hosted test version for just the E75, over on Beta Labs. This is the only S60 phone (so far) with permanent full access to Nokia Messaging as a service, but presumably functionality from this will spread in the coming months, as well as it getting wider compatibility. More details below, if you've got an E75, if use either Yahoo Messanger or Ovi Chat, if you don't mind its Java nature, and if you fancy giving this a whirl.

"Nokia Messaging now offers a desktop-like IM experience on your Nokia device.  You can stay in contact with your friends across multiple communities, easily switch between and save conversations and login invisibly. 

• Chat with your friends on the Yahoo!® Messenger and Ovi communities
• Quickly navigate through multiple conversations across different communities
• Background notifications of new IMs for true multitasking on your phone
• Familiar and integrated community experience -Yahoo-specific emoticons, graphics, and sounds
• Rapidly set status and availability, and login invisibly - choose who you want to talk to
• See your Ovi friends' avatars and set your own
• Save conversations to remember your chat sessions 

This beta is available for the E75 device only, and works with Yahoo!® Messenger and Ovi accounts."