gaim does not support converting a one-on-one conversation into a multi-person chat, you can however right-click someone and Initiate Chat to start a multi-person chat in MSN, and you can use Buddies->Join a chat to start a chat on the other protocols.
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I'm wondering how do I add another person to an ongoing conversation?
In MSN Messenger this is possible so Gaim must support it AT LEAST for that protocol, and any others that support the feature.
Are there any plans to include this 2.x if its not in 1.5.x?
gaim does not support converting a one-on-one conversation into a multi-person chat, you can however right-click someone and Initiate Chat to start a multi-person chat in MSN, and you can use Buddies->Join a chat to start a chat on the other protocols.