From FON Wiki Beta

Connecting to FON_ signal via OSX Leopard

This guide is to help anyone having trouble connecting their machine running OS X to a FON router. This guide is made using 10.5 Leopard but it is the same with 10.4 Tiger.

Ensure you're wireless card is active by clicking on the Wireless Symbol up the top right of the screen and select Turn Airport On if its not On already.
Once the wireless card is on, clicking on the Wireless icon on the top right, will allow Leopard to scan for wireless networks for a few seconds. This will show the wireless networks in range of your computer. Select Fon_ signal and wait for your computer to connect. It should take about 20seconds.
To make sure you are connected to the FON_ signal click Wireless icon on the top right and you should see a tick beside FON_.

Connecting to MyPlace via OSX Leopard

If you have a Fonera yourself you will want to be able to connect to the Private Wireless network for your. It is the same as connecting to FON_AP but select MyPlace instead. A prompt will appear asking you to enter your WPA key.
If you have not changed it, then it is the serial number of your La Fonera which is available on its bottom. You can change the WPA key by logging into your FON account through the Configure your router Settings Page
To make sure you are connected to the private signal click Wireless icon on the top right and you should see a tick beside it.

Troubleshooting

• if you move the System Preferenses app, it can't remember the wireless networks anymore. Like the person in that forum I had put mine in /Applications/Utilities instead of keeping it in the main Applications folder. Now it's back and everything works perfectly! (MacForum - FON Forum)