My phone shows no service even when it has the sim in it.ehy?

Before trying some of the solutions below, make sure that you’re using your phone in an area within your network’s coverage. The cellular signal bars on your iPhone’s should serve as a sign that tells you how strong or weak is the network signal acquired by your iPhone at the moment. If the signal strength indicator is too poor or weak, then that’s likely the main reason why Cellular Data couldn’t get to work as intended. But if mobile data isn’t working even if the signal strength is strong, then the problem is likely within your iPhone system and that is what you should try to rule out. Here are some solutions you can try to fix the issue you're having: 

Solution 1. Restart your iPhone 

1. Press and hold the Sleep/Wake button until the red slider appears. 
2. Drag the slider to turn your device completely off. 
3. After the device turns off, press and hold the Sleep/Wake button again until you see the Apple logo. 

Solution 2. Toggle Cellular Data off and on 

Solution 3. Toggle Airplane Mode on and off 

Solution 4. Reset network settings 

Solution 5. Remove then reinsert the SIM card 

Solution 6. If you still couldn’t get cellular data to work on your iPhone after iOS 13 update, try resetting your device. 

You should reset your device as a last resort and only if you can't restart it. 

To reset, press and hold both the Sleep/Wake and Home buttons for at least 10 seconds, until you see the Apple logo. 

Hope this helps!