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To send a text message, even if you have no signal at the moment, you can type the message and have it waiting in the "outbox"...If the phone sees a usable signal, even for a moment, it can send the message.


And let's not forget, the store-and-forward capability exists from the network to the recipient as well. If the recipient's phone is off or otherwise not reachable by the network, the system will try to deliver the text message the next time the recipient's phone connects to the network. It's not totally foolproof since different networks will expire a message after checking if the recipient is on the network a certain number of times or after holding onto the message for a certain length of time.