Q: Since updating to iOS8 my iPad keeps displaying No Simm every 30 minutes or so

Hello there, Paul.

The following Knowledge Base article provides a great checklist of steps for troubleshooting issues with the "No SIM" alert message appearing on your iOS device:

If you see 'No SIM' alert on iPhone

http://support.apple.com/kb/TS4148

If you see any of the above symptoms on your iPhone, follow these steps:

1. Update your iPhone to the latest version of iOS.
2. Turn airplane mode on and then off again.
3. Restart your iPhone.
4. Check for a carrier settings update. Go to Settings > General > About. Install any available update.
5. Remove the SIM card and make sure that it's a valid SIM that your carrier provided. Also make sure that it's not damaged, worn, or modified. Then reinsert it.
   A SIM tray that comes with one iPhone model won't necessarily work with a different iPhone model. When you insert the correct SIM tray, the SIM tray should be flush with the device.
6. If you have another SIM card, insert it. You can use a SIM card from any phone with the same format as your iPhone SIM card. If your iPhone works with that SIM card, contact the carrier that issued your original SIM card.
7. Restore the iPhone.

If you still see the issue, contact Apple support.

Thanks for reaching out to Apple Support Communities.

Cheers,

Pedro.