Thank you very much for pointing out this issue. I will forward it to the product team and they will look into it as soon as possible.
Did you create another account for mobile use or you used the same account then on your desktop?
I've got exactly the same problem. I use Unlimited World monthly plan but Skype for Windows Phone does not allow me to make a call. It shows "You have insufficient Skype Credit to make this call, Check your account and try again.".
Thus, I check my account by Skype for Windows Phone. Of course, I know I have zero credit as I always have but it did not show my unlimited world plan either.
Hope you guys can solve this problem very soon.
Please can you post your account name you used to log in to Skype on WP?
Thank you. Can you also tell me the destination country of your calls?
Thanks a lot. We will investigate this.
I am very sorry for the inconvenience.