well, you should obviously be able to use your Citycell ZOOM or any CDMA Modem in MAC operating system. All you need is that your modem's driver for MAC. For that you can get details from modem manufacturer website. If you can't find any information, either contact manufacturer support or search for the driver in Google, you can also find some generic driver from MAC forums or at least information.
Below links might be useful in this regard,
http://homepage.mac.com/jrc/contrib/mobile_office/
http://www.engadget.com/2005/01/18/how-to-use-your-cdma-cellphone-as-a-usb-modem/
http://www.experts-exchange.com/Hardware/Networking_Hardware/Modems/Q_22552246.html
http://forum.soft32.com/mac/CDMA-modem-Mac-ftopict108846.html