NO PORT ON MY ISP MODEM(JUST USB & PHONE LINE) TO CONNECT WIFI NETWORK CABLE TO HELP!?

I bought a BT La Fonera+, Wi-Fi Router to connect wirelessly to my laptop. It came with the router, network cable and charger etc. Instructions say to connect the network cable to the isp modem and to the router. Now here’s the problem the isp modem does not have an ethernet port it only has a usb to the home p.c and phone line port to socket is ther any way of getting an extension or multi port hub ?? so i can attach the routers network cable to the modem. Thank you for any help and directions James *Modem is sagem f@st800-840 (blue)