Samsung Galaxy S26+ cannot make calls or send messages

Calls and messages on a Galaxy S26+ fail for the usual reasons plus a few that belong to a very new phone. The S26+ uses a physical SIM and an eSIM, so check in Settings, Connections, SIM manager that the right line is set for calls and for messages, because a recently activated eSIM that is not selected sends nothing. Check Airplane mode and Do Not Disturb, and that Wi-Fi calling is on if the signal is poor indoors. Owners of One UI 8.5 phones describe calls where the other person cannot hear them, which is usually the Bluetooth microphone issue covered on the microphone page, so make a call with Bluetooth off to rule it out.

For messages, open the Messages app, check RCS chat features show Connected, and clear the app's cache.

Install the carrier's settings if the phone prompts, and update the phone. If No service shows everywhere after a restart, the SIM or eSIM profile needs the carrier's attention, and a new SIM often cures it. If the phone shows full signal but calls fail with a message about the network, Wi-Fi calling and VoLTE may be mis-set; in the Phone app's settings turn Wi-Fi calling off and on, and check that Voice over LTE is enabled in Settings, Connections, Mobile networks. Roaming settings matter abroad. Check the S26+'s Phone app settings for Call forwarding and for the Block unknown callers option, because a forwarding rule left over from a previous phone sends calls elsewhere, which looks like a failure to ring.