Is your cellular connection is weak or sporadic in your area? As carriers are moving to 4G LTE, coverage may not be good in some areas of the town. You may want to change from 4G to 3G to get consistent signal.
It is easy to change or switch from 4G LTE to 3G on Samsung Galaxy S3. It might also work for most of the phones. You don’t need to root your phone.
On your android phone, Go to Settings > More > Mobile networks > Make sure “Use Packet Data” is checked. This option allows your phone to connect to your carrier wireless network.
Tap on Network Mode to select LTE/CDMA or CDMA. If you select LTE/CDMA, it will connect to LTE (4G) when its available. You need to select this option ideally if its not already selected. But If you are experiencing connectivity issues
with network, select CDMA option to connect to 3G network only.
Also, CDMA option is useful if you think your battery is draining because of LTE connection.
You can try android app 3G/4G toggle to switch between 3G & 4G quickly. This android app may not work on all android apps.