With the mobile devices enabled with 4G, it is possible to switch on 2G/3G network.
How to proceed?
If the handling depends on each wireless device model, generally you must:
Go to Settings> Mobile networks> Network mode preferred
Choose a GSM (2G) and WCDMA (3G) network, (LTE is 4G)
Accept the new settings. If you want to enable the 4G again, simply re-select an LTE network.
We recommend that you always enable at least the GSM network because there are still areas without 3G (WCDMA) access.