Restart your phone
Your phone might hang-up or freezes because of too many applications being used or too many system services are running. Try to restart your phone. Turn it off and turn it on again.
Check your phone signal
Signal is low in highly rural areas. If you're in the mountain, don't expect a good quality signal. If you're inside a closed room, signal is low. Go outside the room to get better signal. So check your phone signal before complaining that your not able to send or receive text message.
Check your inbox
If your inbox is full (full of messages), it's surely cannot receive a text message. Delete some old messages to free up some space for new messages.
Check call barring service
Find the call barring service on your phone's settings and deactivate it. It should not be active.
Turned off airplane or flight mode
Turn off the Airplace or Flight mode setting of your phone.
Remove Sun Cellular sim and insert to a different phone
Your phone might have a problem with its signal. Remove the Sun Cellular sim from that phone. Try to use another phone and insert the Sun Cellular sim.
Replace Sun Cellular sim
Your Sun Cellular sim might be damaged or broken, replace it by buying a new one. This is the last option.
Do you have any other solution in fixing this type of problem (Sun Celllar sim cannot send/receive text message)? Just post them in the comment below.
Or do you have any problem related with Sun Cellular Sim? You can also post them in the comment below.