Please don't tempt me like that I can't afford to replace my camera after I break it by opening it up.
I'm not thinking about a flash the size used in a proper camera, more something like what the sonyericcson K800 had (it took great pictures at only 3Mpix). On the outside it took about one and a half times the space the two leds on the N900 takes, don't know how much it required on the inside though.
Obviously led flash is cheaper and/or easier to put in a phone, so I guess it comes down to cost, personally I'd pay a little bit more if I could leave my camera at home most of the time.