Linksys WRT54GP2 Setup Manual page 2

Step 5.
Unplug your existing telephone handset from the wall socket.
Reconnect your telephone into phone port 1 on the back of the router.
Step 6.
Connect the power supply and switch the device on.
Now Switch on your computer and modem.
Step 7.
Open an Internet Explorer web browser on your computer and enter
192.168.15.1 into the address bar
Phone Port
Power supply port