| || |
I'm not too sure why you would want to do this since your phone would be in transmit/receave mode longer using more battery life but anyway terpitude is mostly correct.
On GSM networks such as T-Mobile or AT&T there is generally three speeds, GPRS (2g <56-114 kbs), EDGE (2.5g <256 Kbits/s), UMTS/HSPA (3g theoretical max 28 Mbits/s). CDMA networks like Verizon and Spring have generally stuck to just two speeds, cdmaOne (2g 115 Kbits/s) and cdma2000/EVDO (3g theoretical max 14.7 Mbits/s).
Probably what you are refering to as 2g is EDGE on AT&T since that's really the only 2g technology that was ever hyped because that was the best the I*hone could do for the first generation. Verizon generally brands there cdmaOne/2g service as 1x which you will see your phone switch into if it can't find 3g (shows up as 3x which is a little confusing because it's not 3x anything). I'm not too sure why the GSM providers allow you to turn off 3g service. I could that most GSM shares it fequencies with voice, gprs, and EDGE, but has to use a completely different radio with different frequencies for UMTS/3g because their original frequency spectrum didn't have enough bandwidth for 3g. The can probably turn off that different radio to save power.
Verizon on the other hand had enough bandwidth in the single frequency spectrum that they own so they are probably only using one radio for voice, 1x and 3g. In this case you can't turn of 3g because that would turn off voice and 1x too.