YIM really did try to monetize, they just failed.
I also remember MSN messenger trying to monetize VOIP ala Skype but failing. NAT has just been introduced and traversal techniques where half baked, so getting VOIP to work at all was mostly failure. Indeed the primary reason I used YIM was because its voice chat worked.
Unfortunately there doesn't appear to be a good history of what the various IM platforms offered over time, so finding references is hard. :(
BTW: Meebo rocked! I am still annoyed that I have no proper multi-protocol IM program. I've lost contact with people I had been in touch with for over a decade. :( Meebo was the first time I realized that Web Apps could be a Good Thing.
Unfortunately with Meebo's closure I also learned the down side of Web Apps.