How to make a phone call and send a text message?

Cell phone calls and text messages are actually spread by electromagnetic waves.

The mainstream mobile phones are GSM and CDMA, one is frequency division multiple access and the other is code division multiple access.

Simply put, the digitized sound signal and information are carried on an electromagnetic wave with different frequencies or symbols, sent to several base stations, and then decoded on the other party's mobile phone or telephone, and the other party will hear your voice or receive a short message.