To activate the module, you must send an email to your account manager via sales(AT)crm-pour-pme.fr (replace (AT) with @).
To then allow the concerned users to use this function, you must:
Go to the administration area of Simple CRM: Top menu -> Admin -> Settings: then enter the email and pass you use for your SMS subscription.
Then go to the user profile(s) to authorize: Top menu -> Admin -> User list -> Select a user -> Check the box "Allow SMS sending".
The module will then be active and accessible either directly from the SMS icon next to the mobile phone numbers, or from the Application Launcher -> Tools -> SMS.