Apple just announced a media event on the 4th of October, 10:00am local time, at their headquarters in Cupertino, CA. The topic of this event will the the iPhone.

Therefore, the four icons depicted on the invitation tell you everything you need to know (especially if the clock reads 10, as in "October" as well as "10:00"). When, Where, What/Why. (The "Who" is implied by receipt of the invitation, of course). Brilliant.