I am using ubuntu 12.04 on a virtual box with osx as a host. I tryied to run iwconfig, but I can't see any wireless extensions. But my wifi is working using my ubuntu machine! How can I manage this ?
If you run any OS inside VirtualBox, it will not have access to the real hardware (e.g. no access to your WiFi card/USB stick), only to virtualized devices. Thus, you can only manage the Wireless interface from the host system (OSX) and share this network connection via the various options VirtualBox offers.
An exception would be if you had an USB WiFi adapter, because you could pass this through to the VirtualBox. But really, unless it's for testing if something very special works, this is quite unusual and not necessary.