With just an IP set, you can only ping the other end and stuff on that network. To connect to other networks via it, you also need to set up a route. (and DNS to use names).
Having two internet connections complicates things. Disable your eth0 first, then play with usb0. If your phone offers DHCP, you can do via cli what vinnie wrote above, udhcpc is the bundled dhcp client.