In theory, this is doable, however, I'm certainly not good enough to directly help with this. I do think it might be possible to be done if there's a chat service out there that uses an open JSON API, as someone, if I remember right it was GameGuy, already made a JSON encoder/decoder, so it might not be that far of a stretch to figure out the proper way to post/get the JSON data back and forth to an existing chat system. It might be tricky to figure out whispering to just your party, but, most chats out there support direct whisper messages, messages to just friends, and global messages to entire room.