Do I have to enter true data into the system (private email address and work telephone number)?

In terms of provisions of Section 11 of Act No. 428/2002 Coll. on personal data protection as amended:

"Only true personal data can be entered into an information system. The person who entered the data into the system is liable for their incorrectness.” 

The university protects your personal data and does not provide your private email address to other subjects, nor publishes it anywhere.  The work telephone number (mandatory only for employees) will be used for creation of internal telephone book which will be accessible only to university employees and students. This way the responsibility to update the work telephone number is fully on the employee and the updated data in the telephone book will be kept.