Blackberry Cdma Or Gsm

What does it mean when it says "This phone supports both CDMA and GPRS / GSM?

Does this mean he has CDMA and then someone there inside there is a SIM card? How does it work and make it somehow choose which one to use? I'm confused. Specifically I'm curious about the 8830 by BlackBerry ® by Sprint.

it simply means that the phone supports CDMA GPRS / GSM. you can activate the GPRS on yur phone and you surf the Internet via WAP. Short for Code-Division Multiple Access, a digital cellular technology that uses spread-spectrum techniques. Unlike competing systems, such as GSM, that use TDMA, CDMA does not assign a specific frequency to each User. Instead, every channel uses the full available spectrum. Individual conversations are encoded with a sequence pseudo-random digital. CDMA consistently provides better capacity for voice and data communications for other commercial mobile technologies, allowing more subscribers to connect at any time, and is the common platform on which 3G technologies are built. Short for Global System for Mobile Communications, one of the leading digital cellular systems. GSM uses narrowband TDMA, which allows eight simultaneous calls on the same radio frequency.

BlackBerry Storm 9530 (Verizon) – Unboxing and Hands-On Pt 1