How about a loyalty program that automatically reduces your bill (to a maximum of course, we wouldn't want Koodo to go bankrupt because of customers staying forever and not generating any funding for Koodo!)
It could work where after a year of paying your bills on time and in full, for example, you are entitled to one free month of your plan. 2 years = 2 months and so on (again to a maximum). Maybe being entitled to a percentage per year (ie, 1 year = 2% , 2 years = 5%).
Happy loyal customers are the best publicity. You'd rather hear a great deal from your friend than some salesman (we always ask what the fine print is!)