The Smart Network can be used as a relay signal for Sun Cellular subscribers located in areas where network signal is very weak or undetectable. The phone becomes roaming and can send messages through Smart Network, which has wider signal area coverage than Sun Cellular in most places in the Philippines.
Configuring Your Phone
Find the mobile network settings in your Android phone. Usually, it can be accessed via Settings > More settings > Mobile networks.
Make sure your phone connects using GSM signal. Click Network mode > select GSM only. Go back.
Connect to Smart
You are now ready to connect to the Smart network. Click on Network operators > Your phone might begin searching for all available cellular networks in your current location. This could take about 10 seconds.
Select Smart if you find it listed. If not, try searching again by clicking Search networks.
If Smart is still not listed, then there is no Smart signal in your current location. Try searching again in another location until you find the Smart signal.