Bysky

Bysky is an application for smartphones that allows you to send FREE text messages to various satellite phones, such as Iridium, RockSTAR, Inmarsat, Thuraya or Globalstar. Bysky uses your phone’s internet connection (4G/3G/2G/EDGE or Wi-Fi if available) to send messages and receive responses.
You can use your existing address book. If you save a satellite phone number to your address Book, Bysky will automatically determine its type.
To send a free message to a satellite phone – just start a new chat.
Now it's much easier to communicate with people, even when they are far away. You can always start a free chat with a satellite device, and all answers will be received to the same chat.
You can start a group chat and send free text messages to several satellite phones at once.