Four free months of Google Play Music now offered for new subscribers
The conditions of the deal/s may have changed since the initial publishing of this post.

However, it looks like the Mountain View company wants to enlarge its pool of subscribers by running a promotion on its music service. For a limited time, Google offers new customers four free months of Google Play Music instead of just three.
Nothing else changed regarding the service's price, so you'll still have to pay $9.99 after the four-month trial that Google is now offering. Keep in mind that the promotion is aimed at new subscribers, so if you've been paying for the service and stopped at some point, you won't be able to take advantage of the offer.
source: Google Play Music via AndroidPolice
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