Hi,
Currently we don't have a direct command that will send an SMS after booting up. But if you're using SIM Card as WAN source, we could do Events Reporting that will send an SMS if the Mobile Connection is Up replicating the event of a successful boot up with a slight delay.
To configure, access the router's WebUI -> click Services -> Events Reporting -> click Add
Then a tab will open. Please use the guide below for further configuration.
Click Save and Apply. If all configuration are correct, you should be receiving an SMS after a successful boot up. For more information about Events Reporting, click HERE.
Hope this helps.
Regards,
Janmiguel