They may have changed the name since I signed up- I only renew once a year. Normal skype is free- just a name, and you can voice and video chat comp to comp.
Skype in is.. like 60 bucks a year, and gives you unlimited incoming calls, voicemail, and a real live, can dial it from a telephone number. Mainly tho it's a normal phone number- just like any other VoIP dealy.
Skype out is just credit to spend calling telephones- landlines and cells. Like prepaid cell phone credits, only on the computer.
If you have unlimited cell and are staying in the US, then the phone number is probably not needed. I have it because I use it for my permanent phone number, and because I have a pre-paid, cheap cell. It's the whole budget thing- my whole "phone" bill averages about $22 a month, and my mother knows how to call me no matter where I am- a def. plus, since she's a near total technophobe.
Clear as mud?
-j.