Earlier today i was out in the sun, using my iPhone. And then i saw something weird over the speaker. Could this be a second camera... maybe for video conferencing?
It is only visible in the sunlight or under a lamp.



And this image is from the iPhone Help-thing in iTunes, but I guess it's only the camera on the back.

Its probably the sensor the turns the display off when you put phone to ear

it is supposed to have an ambient sensor also i think, so perhaps both?

It's the ambient light sensor, which is the infa-red sensor, next to it is the infa-red LED. (it's much like the way you optical mouse is activated for idle state to working state when you put it sensor to near the surface!)