The GSM setting will give you access to 2G (and 2.5G) data networks using GPRS or EDGE data standards and speeds.
WCDMA will give you access to 3G networks (using either normal 3G or HSDPA standards and speeds).
Both GSM and WCDMA used in mobile telecommunications. The difference is they are used in 2G and 3G.
The primary reason why telecommunications companies are having problems with rapidly deploying is the difference in the frequency bands they use. Because of this, GSM only phones, cannot communicate with WCDMA only networks and vice versa. In order to circumvent this, it has become common for most phone manufacturers to include multiple frequency bands for both 2G networks and 3G networks. This ensures that their mobile phones can be used in almost any network and any location in the world. Telecommunications companies need to deploy a WCDMA network over their existing GSM network to provide 3G services while still maintaining compatibility with older mobile phones that are not compatible with WCDMA.
In mobile phone the normal setting would be Auto, which lets the phone automatically select the best (normally fastest) data network that it can pick up in the area that you’re currently in, but as this involves using all the 2G and 3G chips and antennae this uses more power than forcing the phone to always use one or the other.If available 3G network only pick 3G and ignored 2G.
The downside to picking GSM is that it will stop your phone connecting to high speed 3G data networks, but will save power as the 3G (WCDMA) chips and antenna won’t be used.
The downside to picking WCDMA is that it will stop your phone from using 2G networks at all (so if you’re in an area with no 3G support, then your phone will have no data signal) but if you’re in an area that you know has good 3G signal, then selecting this will save power.
1.WCDMA is a 3G technology while GSM is a 2G technology
2.GSM is slowly being phased out in favor of CDMA
3.GSM is still more widespread than CDMA
4.WCDMA and GSM uses different frequency bands
5.WCDMA offers much faster data speeds than GSM