Using it exactly as it is mentioned in manual, something like:
<i:Interaction.Behaviors>
<behaviors:ApplicationBarBehavior>
<behaviors:ApplicationBarIconButton Command="{Binding UpdateTaskCommand, Mode=OneTime}" IconUri="/Assets/AppBar/save.png" Text="Save Task" />
<behaviors:ApplicationBarIconButton Command="{Binding DeleteTaskCommand, Mode=OneTime}" IconUri="/Assets/AppBar/delete.png" Text="DeleteTask" />
</behaviors:ApplicationBarBehavior>
</i:Interaction.Behaviors>
but i'm getting xaml warnings "Path cannot be absolute". In general, it works, but warnings are annoying.
Images properties are set to "Content" and "Copy if newer" like mentioned here: WP7 Dynamic icons in ApplicationBar
OK, so updating to the latest version (1.4.1 at the moment) solved the problem. Link: https://github.com/Cimbalino/Cimbalino-Phone-Toolkit/downloads
Thanks, Pedro (dunno how to mark comment as right answer).