Samsung Galaxy Note20 cannot make calls or send messages

The checks in more detail

If the other person cannot hear you, test with Bluetooth off and in Voice Recorder to check the microphone. Because the Note20's software has ended, carrier updates and VoLTE profiles may lag behind the network, and some carriers drop support for older phones; ask the carrier whether the Note20 is still supported on your plan. Reset network settings clears the stored configuration. If No service shows everywhere, the SIM or modem is at fault. The Note20's S Pen has Air Actions and Air Command that can send or hold calls only in rare configurations, so ignore them for call faults.

A more useful check is the Phone app's Call settings, Supplementary services, where Call forwarding and Call waiting are shown; an old forwarding rule left on can send calls elsewhere and look like missed calls. Because the Note20 is a large phone used for work, many owners also use it with a Bluetooth headset for calls, and a headset that connects but gives a robotic voice may be using the hands-free profile at low quality; switching the call to the earpiece confirms that.

Samsung's Voice clarity and noise cancellation settings in the call menu can improve or worsen the sound, so test with them on and off. If calls work but contacts' names do not appear, the Phone app's contact sync may be off, which Samsung's Contacts app controls under Settings, Manage contacts, so check it before concluding that calling is broken. Texts from short codes, such as verification messages, can be blocked by a spam filter, and the Messages app's Spam protection settings list blocked senders.