i remember there was a yahoo plugin, not sure, yahoo has some easy activeX controls, even for audio and webcam implementation. and now yahoo can access both clients, yahoo and msn. but why not just use the skype plugin, already in development.
well i was about to use the skype plugin but as far i know there will be no chat option so i decided to go with the .net phone plugin for voice and then msn for chats when needed
as i need to spend money on a umts/3g modem and still have my cellphone adding skype would be a bit overkill as it also cost me a monthly fee... and with skype i only get unlimited phonecalls and option to send sms.. i hardly call people and the sms service i have on my cell phone is almost flatrate.. so adding skype would just be money out the window..
so thats why i focus on msn as it's allready there and i allready have an account for that.. it will mainly be used for short messages to my girlfriend when i'm out or on my way home from work... ot when she is nexst to me and want to chat with friends...