@Lucyzhou
do one thing Make sure your phone is off before removing your SIM card,
and do rebooting your phone take your SIM card out and waiting for a 2 minute and put it back and turn on -This one is quick and simple.
what is mean for Rebooting the phone means to turn off your phone and turn it back on again.
or can you do try reseat the SIM card
1. power off your device
2. take out the SIM card,
3. wipe it clean SIM card,
4. put it back and power on,
5. toggling airplane mode off/on,
and do again Rebooting your phone means to turn off your phone and turn it back on again.
How to reset network settings on an IPhone
Go to Settings > General > Reset > Reset Network Settings.
This also resets Wi-Fi networks and passwords,
or visit HERE
and go Changing APN Settings On An IPhone
click HERE
Ensure you have the correct APN settings by visiting HERE.
Select the brand and model of your phone, After doing so, you will be provided with the exact APNs required for your phone on our network.
for iphone go to Settings > Messages > To turn iMessage on or off,
Turn your data on to send a Picture Messaging in world-wide,
if your data is off and your home internet wifi is on is not going through the Picture or a video Messaging,
you have to do this to is go through you will need to turn your data on to send a Picture or a video Messaging in world-wide,
make sure your DATA is on.
and do again Rebooting your phone means to turn off your phone and turn it back on again.
Good Luck
