I’ve noticed this problem for the past 10 years now, that a VOIP or Skype call will work fine.. and then start to have problems..
Static will show up on the call.. Or it will get incredibly choppy.. Or even disconnect.
What is most likely happening is that your local internet provider (whether wired or wireless) is intentionally scrambling your call. Carriers have the ability to detect certain types of traffic and do things to it when it is in their interests. So while your internet connection may be being used for 8 things simultaneously they can detect the skype traffic and start discarding some of those packets, or introduce static into the line.
You can test this by signing up for a VPN like witopia and make a call. A VPN will encrypt the call so your carrier can no longer detect what is happening. More often than not, the problem will go away. This is a sign you need to change your internet provider. There is no other option. (you should also complain).
One example of when this happened to me was when I was at LAX (LA Airport) and was using my tmobile 4g wireless card to call my brother in Australia. For the first 3 calls the call quality was terrible. Then finally I tried turning on the VPN on my laptop and calling back. The line quality was perfect. The difference was startling.
The carriers will make excuses about this but the reality is – they scramble VOIP/Skype calls so you will use more of their services.