I was going to just listen to the way this thread is going because I find it fascinating, but now that it has been spelled out, I must make a very important distinction between my idea and PGPFone, WebPhone, etc. -- These are Web-based programs designed to speak over very long distances for "free" (neglecting ISP charges, etc.), adding the extra functionality of encrypting your data along the way so sniffers, etc can't listen in on your conversation.
PGPfone works over POTS and IP. It was not originally designed to work over IP. The issues raised in my first post apply to modem/modem connections and IP based implementations. The issues raised in my second post apply to IP based implementations only (that's not quite true, but I don't want to go any deeper into it). --Lucky