September is a particularly slow month for airline travel. Situated between the summer rush and the holiday season, consumers usually take September off from traveling the friendly skies. And incentives to move around during the back to school season are further inhibited by economic constraints happening right now. But JetBlue has found a way to get people into their airline seats: they’re offering unlimited Jet Blue flights for the month of September.

Between September 8 and October 8, travelers can take to JetBlue’s planes as often as they’d like. For only $599. The airline, which is known for its social media savvy, sent out a press release about their offer and tweeted about the deal yesterday. Since then, they’ve sold out 1/3 of their inventory.

According to JetBlue spokesperson Jenny Dervin: “September is a slower month for us. Peak seasons are the holidays and summer. So we thought: ‘Let’s find a way to fill seats.'”

And it appears to be working. To announce their offer, JetBlue sent one tweet to their over 1 million Twitter followers, a general press release and a newsletter to their frequent flyers yesterday.

Since making the announcement, JetBlue has found over 10 million mentions of its brand on blogs and news sites. They’ve seen hits to their trip planning route map grow 861%. Meanwhile, other sites are piggybacking on the deal. For instance, travel mapping site Evelater is encouraging people to post their All-You-Can-Jet plans. They were a trending topic on Twitter yesterday and the positive word of mouth continues to grow.

With an average flight price of $140, it won’t take long for frequent travelers to get their money’s worth on the All-You-Can-Jet plan. And excess interest in the offer could be problematic for the airline’s bottom line. Frequent travelers could be keeping money in their pockets that might have otherwise gone to JetBlue for individual flights. But that is a problem that JetBlue is glad to have. Says Dervin:

“It’s a calculated risk. But it is low enough to not stop us from doing this. We think it’s so innovative that we’ll end up with more customers not fewer.”

To combat completely overwhelming their system (and to ensure people who purchase the plans will be able to book seats) JetBlue has limited the number of passes that they’ll be selling. But after one day, they’ve sold 1/3 of the inventory they put aside. Says Devinl:

“Once people try JetBlue, we generally find we’ve made a customer for life. This is a good way for people to give us a try, especially in a month that has more searts available than any other time of year. If we make a little money that’s great too.”

Most people can’t just up and leave for a month to fly around the country. But the word of mouth the company has received so far has been fantastic. If twitterers liked JetBlue before, they’re simply atwitter now. Just a sampling: