If your phone shows “no network” then you will not send anything for there is no network to carry the call.
What will work is when your phone can hear other networks but not your own, in this case emergency calls can be made. Likewise, you can make emergency calls without a SIM. In both these cases your phone shows something like “emergency calls only”.
This service allows you to send text messages to the 999 service and by registering the phone, the emergency networks know more about you so you don’t have to send as much in the text.