In an effort to better promote BBM Music, Research in Motion’s new social music sharing and discovery service, the company is offering free 4 month subscriptions to users who sign up to BBM Music by Jan 4th.

What is really cool is that RIM is offering 4 free months of BBM Music to both new and existing users of the service…

BBM Music normally cost’s $4.99 per month which gets you access to 50 songs, 25 which can be swapped out each month.¬† BBM Music also allows you to access up to 50 songs from each of your BBM contact’s libraries limiting the amount of music available to you only by the number of your BBM contacts who also use the service.

You can pick up BBM Music in BlackBerry App World or, downloat OTA to your BlackBerry by visiting http://www.blackberry.com/bbmmusic.