AIUI, Android has a "hack" where hardware events will wake the phone for a few seconds, "hoping" that is enough time for the corresponding process to catch the event and decide whether it wants to keep the phone awake or not.

If the process (e.g. Skype answering to TCP traffic) does not have enough time, the phone may very well suspend while Skype is still trying to show its UI, missing the incoming call altogether.

(Sounds terribly racy to me, but I suppose that with a big enough timeout chances for a race condition are minor. Yet another reason Android's power management _sucks_).