Google Pixel 4a (5G) cannot make calls or send messages

The checks in more detail

Google's mobile connectivity page lists these steps in this order. If calls drop at home, turn on Wi-Fi calling in the Phone app settings and in Settings, Network and internet, Calls and SMS, which uses your Wi-Fi when the cellular signal is poor. If texts fail, check Messages settings for RCS chats and that mobile data is on, as MMS and group texts need data, and clear the Messages app's cache and restart. In Settings, Network and internet, SIMs, Preferred network type, try 4G only if 5G is weak where you are, since a phone that flips between 5G and 4G drops calls.

Check Do Not Disturb and blocked numbers. If you switched from an iPhone, deregister iMessage so that texts reach you. Reset network settings in Settings, System, Reset options if the problem stays, then restart. Ask the carrier whether your line has a block, an outage or an unsupported device, since carriers sometimes retire support for older network types. If no SIM works in this phone, the modem or antenna may have failed, and with a phone of this age, replacement may be sensible. Back up before any repair. Keep a note of when and where the fault happens, since a call that fails only in one building is a coverage issue and not a phone fault, and the carrier can often help with a booster or Wi-Fi calling.

Test calls to several numbers and on both Wi-Fi calling and cellular. If voicemail does not notify you, check visual voicemail is set up and that the Phone app has notification permission, which an update sometimes resets. Check voicemail too: visual voicemail needs the carrier's service and the Phone app's permissions, and a full mailbox can make callers hear an error and think the phone is off. Delete old messages, set up the greeting again and confirm that call forwarding is not turned on by accident, since an unconditional forward sends every call elsewhere and makes the phone seem silent. These small settings explain many cases of missed calls.