As soon as you've purchased the telephony module (CTI-Module) you can activate the module in your configuration. Point to Edit -> Configuration in your project manager in Xpert-Timer, then point to Additional and check the box for "Telephony".
Additionally you need to activate the telephony for each user. Depending on how many licenses you've purchased, you can activate them in the user settings. Point to "Additional modules" and activate the telephony for the user.