What Skype credit is - is that you "prepay" for placing telephone calls from your computer. That is, if you wish to call a phone number, say a client's telephone number in France, you use your Skype credit. However, if you place a Skype-to-Skype call to that same client, the call is free. Each of you has to agree to accept being connected on Skype (sort of like connecting on Facebook, LinkedIn, etc.).
The prepaid credit deal is very much the same thing as purchasing a pre-paid calling card. You buy a certain amount of "credit minutes" and once you use them up, you need to replenish if you want to keep making those calls. I used this for two years while my daughters were studying in the UK. I couldn't have lived without it! But the CRITICAL point to remember is that SKYPE is free when making skype-to-skype calls. You only use your credits when you call from your Skype account to another TELEPHONE number.
I love Skype and I encourage everyone I associate with to use it. I like dealing with people face to face. (And believe me, once you establish a relationship, it is not awkward at all to speak via video -- it's fabulous! Just keep a little makeup kit handy to throw on some lipstick -- just because

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There is also an add-on to Skype called Pamela which allows you to record your calls. I'm just throwing that in, as it is not free after 15 minutes of recording. But it is useful for certain clients who need to record statements. And now I'm getting off subject ... You can see I love Skype!