The below is for use with an IsatPhone:
The easiest (and FREE) way to send a text to an Inmarsat IsatPhone Pro is to use your email client software.
Step 1: Open your email program; Outlook, Gmail, Hotmail, etc. and proceed as if you were sending a regular email.
Step 2: In the email address field; enter the IsatPhone Pro # ( Example: 87077642xxxx), the # will begin with 8707 and it will contain 12 digits. Then add @message.inmarsat.com after the IsatPhone Pro number.
Step 3: Complete the text or SMS message in the body of the email, but remember you only have 160 characters.
Step 4: Send the message as you would send a regular email!
The below is for Iridium Satellite Phones: