1. Go to Network Settings. Each cellphone unit is different. Your network setting could be found in your Settings, or in Connectivity. Read your phone's manual if you can't find your network settings.
2. Go to Network Preferences. In some cellular phones like Nokia, this menu is called operator settings. Here, you can choose between the Automatic or Manual network settings. Choose Manual.
3. Your phone will scan for the available networks. After finishing the scan, look for and choose the Smart network. Yes, you should choose the SMART network for your sun cellular sim.
4. You're done!
5. After registering your network settings to Smart, you can now go back to Automatic settings. Your phone will now automatically connect to either sun or smart network depending on your location's signal.
Good luck!