The service is in closed beta and you have to take a survey first and sign a non-disclosure agreement with Skype to test it. You’re then entitled to an unspecified amount of free Skype credit for calling landlines and mobiles as a thank you gift. In addition, a “larger gift” will be given to the top contributor.
Successful applicants will be contacted over the next few days and you can get started with the survey here. Remember that it’s only open to Mac users.