I'm not sure if this is what you're talking about or not, but I bought a subscription for Skype once when I was on a 5-week mission trip in France so that I could phone home while I was there. My subscription was a flat amount for a certain number of minutes, though, but I know there are different types of subscriptions. Anyways, I made calls just fine with it so I think you should be able to also

I never bought the subscription for a specific number or numbers, though, and while I don't know this for sure, it seems to me like if you called their Skype account, you would be calling to their actual Skype account and not the phone number. I think your best bet if you want to reach the phone number is to just directly call that.