How do I stop iPad telling me I have no SIM card installed

Depending on your iPad model, if you have Siri you can tell her to turn Cellular Data off. If you own the iPad 2, then the only way I was able to do it was to get a SIM card (you don't need to activate it) and place it in the Sim slot. Once you do that, you then have access to turn off cellular data through settings.

Settings->Cellular Data - toggle it off.

Hope this helps!

If you don't have a temporary SIM available to enable the Cellular Data settings to get to its on/off switch, this is what worked for me:

1). Turn on Airplane Mode and wait at least 15 full seconds (really) to allow the wireless radios to truly shut down. This will buy you time in step #2.

2). Turn Airplane Mode back off, and IMMEDIATELY tap on the greyed out Cellular Data option. If you can get focus to this option during the split second before the iPad realizes there is still no SIM, you'll see all the Cellular Data options appear on the right, including its on/off switch... but all greyed out. Getting warmer though.

3). Repeat step #1.

4). Turn Airplane Mode back off once again, and this time, try to quickly dismiss the "no SIM installed" message and tap on the Cellular Data on/off switch. For a split second, it may be lit and accessible. If not, try again. This part can be frustrating, and may take quite a few attempts.

If you can get it turned off, you should stop seeing the SIM errors.

My environment for reference: Original iPad 2, iOS 9.0.2

Paul