Apps can't elect to be started up when the phone boots, nor can they count on avoiding being killed if the user is running a graphically intense game or something.

Except VoIP apps, since we want all apps with that capability to start on boot even if we only use them once a month, and we don't want any others to start on boot even if we use them daily. iOS regulations are so stupid.

Backgrounding the app closes all its sockets, or you cannot rely on them to stay open except for VoIP apps.