When I say "excuse myself" I guess I really mean from any significant conversation. I may continue to spend time with people who behave like this, but I back out of any serious discussions if they are conducted with interruptions from personal devices.
Smalltalk is easy and requires very little thought or concentration anyway, but I no longer give my full attention if it is not reciprocated.
I don't make a point of doing it, but if I am left hanging mid-word while someone checks their phone, and they subsequently attempt to pick up the thread again, I just change the topic to a bullshit one (How 'bout that game on the w'end?).
As regards my own behaviour: I keep a smartphone, but I have no notifications for email or SMS. I'll receive an interrupt for a phone call (something my relatives only tend to make in emergency situations) and that's it.
I think that, for me, this is the ideal balance between giving my full attention to conversations and being contactable.