If you are after price certainty you can choose from 3 calling plans that include calls to local, national and mobile numbers.
Calling minutes: 5,000 mins Local, 1,000 mins National, 250 mins Landline to Mobile
Calling minutes: 10,000 mins Local, 2,000 mins National, 500 mins Landline to Mobile
Calling minutes: 20,000 mins Local, 3,000 mins National, 1,000 mins Landline to Mobile
Alternatively, you can opt for a usage based plan, where you pay per minute.