$0 means the UPFRONT cost.. and that only applies to certain phones (often the better phones still have an upfront cost).
The tabs (small-medium) will be between $4-15 extra per month for 24 months depending on the phone.
Its not a contract specifically its a promise to pay off the tab over 24 months (adding $4-$15 to your monthly bill).
It can be paid off at anytime though if you want another phone or to move to another company.
Check Koodo website or your local retailer for the price of the phones.
https://www.koodomobile.com/phones?INTC ... hop_Phones