The Block can be configured to show contact methods including: Email, Message, and Phone number, the user Profile picture and online status - similar to Skype, Facebook Messenger, etc.
Due to the fact that the Block displays personal information from Profiles (email and phone number in particular) it should not be used in Courses that allow Guest access for obvious privacy reasons. The developers make this clear - good
It might be possible to replicate/access the functionality of this Block in others ways within Moodle, but the effectiveness of the Block is that it gathers information and communication methods into one location - so where appropriate, perhaps in courses with high interaction, it will be very useful indeed.
You can try this Block yourself for real on our public plugins site: http://plugins.moodlebites.com