This is weird. My iPhone has done this only twice, but has been reformatted between occurrences. I don't know what causes it, but once i saw it as it happened: when the screen is woken and unlocked, the home screen icons appear to "squish" downwards to make space for O2 to be written under the time!? No idea what causes it/why it is there, but once i restart my iPhone it disappears and the screen returns to normal. Just wondered if anyone could shed any light on it or if anyone else has experienced it.