You can select which network modes your tablet can use, eg. 3G or GSM. Your choice determines the data speeds you can achieve.
Tap the time in the bottom right corner of the display.
Tap More settings.
Tap Mobile networks.
Tap Network mode.
Tap LTE/GSM/WCDMA (Auto mode), GSM only or WCDMA only.
3G (UMTS) or 4G (LTE) enables you to achieve higher data speeds than when using 2G (GSM). If you select LTE/GSM/WCDMA (Auto mode), your tablet automatically switches between the three network modes provided you're within range of a 3G or 4G network. If you select GSM only, you can't achieve high data speeds. If you select WCDMA only, your tablet can only connect to 3G networks.