Hacking an analogue line would require access to the physical cable which is actually fairly easy to do if you know what you are doing. Its often patched into a fairly easily opened cabinet in a public location.
In order to hack into a voip call you need access to a device which is along the data path the call makes otherwise you cannot 'see' the traffic. There are tricks you can do if you are on the same local network but generally for home internet connections this is very difficult to do. The main way it would be done would be to try and install some software on your local machine by trying to trick you to install it or to break into the house.
If you want to be secure get a hardware voip phone which supports encryption and make sure other computers in the house are switched off (incase they have spyware installed to intercept network traffic)
