How to prevent blocking mobile phones?

I can't prevent it, but now GPRS network is generally used to prevent it, so the landlord can only use 3G network when he wants to be blocked, and basically he can barely communicate. Sending text messages is no problem. There was a classmate in the class who pretended to use 3G to prevent shielding during the exam. As a result, the text message was sent out during the exam, and everything else was blocked. As you can imagine, everyone received his short message afterwards, so the 3G card of 3G network can't be blocked to some extent. You can only find special equipment if you want to reverse gear. The most important thing is that your mobile phone must support 3G network, mobile TD-SCDMA, Unicom WCDMA and telecom CDMA2000. If the landlord doesn't know whether his mobile phone supports it, he can consult in the business hall or check online.