Calling internally with Telzio is free. You can call anyone on your phone system by dialing their 3 digit extension.
This will not use up any of your free minutes or incur any charges.
To dial another person in your office, directly dial their 3 digit extension (on some phones you will need to hit Send to initiate the call).
Extensions are created on the Users page. To create extensions for any desk IP phone or softphone, click on Add User.
See here for help on how to create users.