Ahmad-
I want to caution against using Skype. I find there are Skype issues with interference and noise after about 20 or 30 minutes (using it from different computers and even with from different locations), and frequently find the service (including the paid version) causes me enough problems that it detracts from the interview, and I have been known to disconnect and call back with my cell phone (I know this can get pricy, but that is another issue).
However, for the sake of recording, I encourage you to consider something other than a Skype plug-in. If there is a Skype problem, then the Skype plug-in will also not work. I use an external recorder with an ear-piece, which I discussed on my blog last year
http://silenceandvoice.com/archives/2009/08/10/interview-equipment-for-phone-and-distance-research/, as this flexibility allows me to use Skype, DimDim, or the phone, without any limitations for changing between modalities mid-stream.
Jeffrey