I use a pre-paid, pay-as-you-use phone from 7-11. You need to add money to the phone if either the balance reach $0 (so that you can use the phone) or if it has been an year since you last topped up. If you don't top it up within a year, you lose any money you had in it, and if you do top up, any money you had (along with the top up amount you added) will get rolled over for another year.
The problem is that I rarely use my phone, so I almost always reach the end of the year before reaching a $0 balance. So I have to top up to roll the balance over to the next year. I try to wait until the last moment to top up so that my balance doesn't continue to build too much. So last week I had to top up, and I waited until the last day to top up. The problem is the last time I topped up was an year ago, so I couldn't remember how to! So there I was on the last day before expiry at 10:00 pm trying to remember how to top up my phone. I topped it up, but the balance and the new expiry date wouldn't show ... turns out after topping up, the system sends you an email with a code and a link and you have to go to link and put the code to actually top up.
I did manage to figure it out before midnight so that I could roll my money over, but I'm sure I'll forget it again come next year. Hopefully I'll remember to top up a bit earlier next time so that I leave myself sometime to figure out how to do it again.