As described in this post in androidforums: http://forums.androidcentral.com/google-nexus-4/235432-nexus-4-apps-sleeping-when-screen-blanked.html [androidcentral.com] all apps are put into a sleep state when the screen is blanked. This means that gmail notifications don't happen, and GrooveIP doesn't answer calls. The good news is that Google support was very responsive when I called and told me they would replace the phone.