Currently there is no interface for a telephone system, or at least no full integration. A full integration would be necessary, if it is required, that incoming calls are directly recognized and show the contact in your CRM.
But since CentralStationCRM runs in a web browser, you can make phone numbers clickable at least for outgoing calls, eg via a browser addon. This works well on Voice over IP (VoIP) providers such as Sipgate or Skype. Such add-ons can be found, for example, with Sipgate or vendor-independent for the Firefox browser.
This add on searches, similar to how you might know it from your phone, the whole web interface by digits that look like phone numbers, and make them clickable. It works no matter how the numbers are formatted (eg +44 1234 56789, 123456789 or 123-456789).
For mobile use checkt out our app in the Google Play Store and the iOS App Store.