Best answer by Mayumi
There is no 100 minutes add-on.
There are Unlimited Anytime Minutes Add-on ($20) or Unlimited Incoming Calls Add-on($10)
Minutes overage charge is $0.5/ min. So, If you go over 100 mins > It will be $50 overage charge.
If you are sure going over your minutes, then add-ons helps.
Or you make most calls during your free evenings and weekends and/or call your friends/family through app like messenger if you can access WIFI to save your anytime minutes.
Also if you go over your minutes often, it might be better to upgrade your plan too.