Well this is probably the best way I can think of doing something. It is indeed done through setting up a network bridge. Basically with Windows XP (or any other recent Windows version) and I am making the assumption that you have Windows, you can choose to do something known as Internet connection sharing which will take the internet connection from one source, the Cingular card in this case, and then it will broadcast that signal to another NIC (a regular ethernet card for example) which can be hooked up to another computer or router.
This may help
Computer with an ethernet port ETH0, also with your Cingular card, WIFICARD.
So WIFICARD picks up the signal. It then broadcasts via ICS to ETH0. ETH0 when hooked up to another computer or router will assign the connected item an IP address of 192.168.0.X
Hope you can understand what I am trying to communicate here.
More info on ICShttp://www.practicallynetworked.com/sharing/xp_ics/