I'm bumping this thread. It's been over a year since the original post. This promo is supposed to be good on your plan indefinitely (as long as you don't make any changes), but I've heard other people say they were told it's only for one year. We're past the one year mark, or close to it, so make sure you're checking that this promo doesn't fall off automatically.
Although I'm sure you'll notice if your bill is suddenly $20-$100 more... lol. If you have any issues, give us a head's up on what happened and what you did to "fix it".