I don't know if this was discussed, but I'm going to chime in and recommend that you absolutely make sure your account is set to PAPER BILLING and ensure that they don't have a credit card on your account.
I was doing the 5 month for $20 or $25 cycle for the last 2 years, and I forgot to call last time... Well, they didn't forget, and went ahead and billed me for the maximum account @$120something.
I called in an said I'd like to cancel because I didn't authorize that bill, and the friendly rep was quick to help, give me the $25/5mo deal, and credit me back the $100 difference. I asked about blocking my card, and they said that the only way to make sure you don't get errant re-subscriptions is to make sure you're on paper billing (I was somewhat shocked they put it that way). They even went so far as to delete my CC # from my account.
Long story short, if you're like me and forget everything, get on paper billing and you'll get reminders before your service is up- at which point you can call and make sure you get the $25/5mo or whatever deal you want.
Side rant- does anyone else think its hilarious that buying a YEAR or two years prepaid is more expensive than calling in every 5 months? Last time I was on the phone with them, I made it very clear that I was ready to buy TWO YEARS in advance if they gave me the $5/mo. They won't do it. The best annual rate I've heard of is still $87/mo. Crazy. Who do they think they are, timewarner??