what actually provokes attacks of opportunity?
the verbal or somatic or both? if so if I had silent spell and still spell I no longer provoke?
It has nothing to do with the components. Casting the spell itself is what provokes.
The only ways to not provoke while casting a spell is to either cast defensively (which requires a concentration check, DC 15+ twice the spells level), or use a quickened spell (or other spell with a casting time of a swift action).
To provide some 'fluff' on Jeraa's statement: When casting the spell, you're normally focusing your attention on casting. It takes concentration to do so.
If you're not actively threatened by a foe, then you can do so without worrying; if you're within melee range of an enemy, then you have to use part of your concentration on keeping up your guard - and thus why you have to make a concentration check.
Now... if you're not already -in- combat, I'd say it wouldn't provoke being still and silent, because... until the spell goes off... they don't even know anything is wrong.
But they do know. You can still make a spellcraft check to identify a spell being cast even when there are no components for the spell. You just have to be able to see the spell being cast. That implies that there is something there to see, something that makes it obvious you are doing something, even if you aren't waving your hands and speaking mumbo-jumbo.