[cmsimike]

I will happily replace any third party messenger I currently use with one that sends notifications to all my devices (like iMessage does). I haven't tried this with BBM yet but does anyone know of a third party service that would send messages to all my devices with the app installed?

[modeless]

Google Hangouts

[apunic]

+1, Google Hangout does a great job on this + archiving the conversations in your mail inbox.

Another one is Facebook, where you do not have to request a messaging connection to the other party.