Importing and updating contacts
with 
To automate the import and update of contacts from one application to another.
Emails, SMS and voice messages
with
To automate the sending of messages between Digitaleo and your application.
What you can do with 
Synchronise your contacts on one side only
For example: create a contact in Vtiger when it is created in Digitaleo.
Automate your SMS, emails and voice messages
For example: send an SMS to a contact using Digitaleo when the latter generates an invoice in Vtiger.