If your WL-500g didn't come with CDMA-enabled firmware, you have to flash it to the device. Just go to System Setup -> Firmware Upgrade in the web interface. If the 'Firmware Release' field does not contain CDMA, then you have to download the latest CDMA firmware (http://koppel.cz/cdmawifi/download/) and upload it. The only CDMA-specific setting is CDMA -> CDMA Config in the web interface. Type in your user name and password, save and restart. Then you're ready to plug the modem, which would connect in a few seconds to the provider and Internet will be available on all LAN ports and Wireless.
I have omitted all the generic configuration that is not specific for CDMA. However, it should work fine with factory settings (one recommendation, though: set up some encryption for Wireless or disable it completely, since otherwise you are exposing your network to hackers, neighbours and other weird people )
Should you have any problems with CDMA, use the forum (http://koppel.cz/conferences/). Its primary language is Czech but if you post an English question, someone will definitely provide help.