http://www.nikonchat.com/wireless-nikon-flash/
Do I need a radio trigger to use my Nikon SB 900 Nikon D90 Wireless one?
Need to know if the camera and flash gun can be used wirelessly without buying more stuff. the camera and flash gun That's another thing
Yes you can. Look on page 188 of your user manual D90 and you should be golden.
How To Setup Wireless Flash With Nikon DSLRs
Nikon News