The easiest way to send an SMS message is to use the Inmarsat SMS web portal.

 http://connect.inmarsat.com/Services/Land/IsatPhone/SMS/sms.html

Another way to send an SMS message is to use email-to-text conversion. Just send an email to [email protected] where mobile_number is the 12-digit 870 mobile number of the Inmarsat GSPS satellite phone or Inmarsat BGAN terminal. The email will automatically be converted to an SMS message. The maximum length of the email should be 160 characters.

The maximum length of an SMS message is 160 characters.
There is no charge to receive an SMS message on an Inmarsat phone or terminal.
There is a charge for outbound SMS messages sent from your Inmarsat phone or terminal (see your service agreement for details).

Sending an SMS to Inmarsat