i using a mobile-broad band connection and i installed a Debian on a virtual-box without graphics(the Debian live-CD i created using a live-build tool)now problem is that how can i give the static ip-address using a mobile-broadband connection.i have no Ethernet? plz help me out i am stuck in it.and and second is that my two virtual machines are not ping to each others ? i need yours help very badly?
thanks

I think is actually VM related, not network related.
Any way:
First of all check, if Virtual Machines have network controllers assigned by VirtualBox (in virtual machine configuration), if they have it, then you can easily get IP on machines using dhclient
'-v' flag means verbose, so you would see, if dhclient is getting any response.
Or you can assign static IP (I dislike static IP - it is completely wrong and hard to manage)
Obviously your IP depends on your network, so you have to tune it to your network - this just example