Getting my nikon d3100 to fire my SB700 flash without any cords/wires?

I read on a few blogs that you can do this by turning on the flash on the cam. But I can't seem to get it… Help?

Try cowboyStudio.com.

They sell a wireless trigger for speedlights.

It is possible to use the camera flash to fire a slave which fits between a tripod and the SF700.
Flash-triggered optical slaves can be had for $30.
The added flash from the camera, though, might ruin or aid the lighting, depending on the angles of both flashes.

Have you read your user manual?

Look on page 173

You can use the on-board flash to control the SB700