This is just regular Skype calls to a landline at a cheap rate. I have the option of setting my caller-ID as my mobile number (they send a verification message) or leaving it blank. Obviously it's better to have a caller-ID for most purposes.
So you've subscribed to a fixed number with Skype? If so, which country is the number associated with? Unrelated to this topic, I thought I'd mention I haven't used Skype for years. However, I recently had reason to call a company in the UK and it appears to be impossible to call freephone numbers in the UK from overseas using fixed line and mobile phones, so I turned to Skype as it's apparently possibly to call freephone numbers (for free) via Skype, and it worked!