Are messages sent to a cell phone# sent only when the phone is opened, or what happens when phone is closed?

Answer 1

Not quite sure what you mean. The message is sent to the network within a few seconds after pressing the send button. It is out of the senders had at that point and the sender's phone can be switched off. The receiver can only receive when their phone is switched on. The network will hold the message for a number of days if it can't reach the destination number.