Assuming the modem actually has WiFi in it, probably the problem is that the WiFi access point is set to use WPA2 encryption, as this is usually default, and it is better. However,
Nokia's do not support this - unfortunately they support WEP or open only
🙁
In order to use WiFi on your phone, you will need to change your WiFi access point to use WEP encryption (despite it being worse than WPA2).
To do this, go in to your web browser (Internet Explorer, Firefox or
Google Chrome) and type 192.168.1.1 in the address bar. Log in with the username and password set for the modem (default is admin and admin).
First thing you will need to do is change the modem to use PPPoE. Go to Configuration > Internet Connection
There should be a link to connect underneath "PPPoE_0_35". Click on it to connect. Check that you can get internet connection on your computer (do NOT use the dialer on your PC to connect - the modem now takes care of the connection so you no longer need this. The connection is now just "on" whenever the modem is turned on, so, as long as your network card is configured you should be able to browse without having to dial).
If all this is good, then we can continue.
Next, go to Configuration > Wireless Configuration. Enable the wireless network, select the correct country, change your network SSID to whatever you would like.
Scroll down, and change the security option to be 128-bits. Key method should be probably Hex or something (I'm not 100% sure with this modem). WEP passphrase should be exactly 13 alphanumeric characters. Click confirm.
Then go up to the top again and click on
MAC Address Filter. Disable it (another counterintuative move, but this is what they suggest).
Save all the settings, let the
router restart, and try connecting to the WiFi with your phone.