Knowing the fact that Trilian has already done this since several years ago may not thrill you, but it surprises me a lot knowing that the INITIATIVE came directly from the service providers themself: Microsoft and Yahoo!
So, I can clearly see there's no such third parties reside between, like Trilian (and others I'm not aware of).
For now, if you're using Windows Live Messenger 8.0 (I'm currently using version 8.0.0792.00), go directly signing in yourself here:
http://ideas.live.com/programpage.aspx?versionId=7adb59de-a857-45ba-81cc-685ee3e858fe
and/or
if you're using Yahoo! Messenger (I'm currently using Yahoo! Messenger with Voice BETA version 8.0.0.506), go signing in yourself directly here:
http://messenger.yahoo.com/partners_msn.php;_ylt=AkkG5kKAwQD3Fq1YKTaOJNtwMMIF
I have tried them myself and they simply work great. I can even Nudge [WLM's term] or Buzz!!! [YM's term]. Just try it out yourself!
Personally, I'd like to say: it's about combining the best of breed!
BTW, I can be contacted through:
Don't forget to remove the underscores.