Ahh, but there is specific legislation in place that protects the privacy of the PSTN.  You lose that protection if you make that same phone call over IP.

I’m not aware of any act of parliament that offers you that same protection for Internet traffic

From: Jonathan Woolley [mailto:nznog@jonathanwoolley.com]
…

In my humble opinion this argument is completely bogus. The PSTN is a public network, but if I make a call to my grandfather in England, I don't expect anyone to be able to listen to what I'm saying without a warrant. If I have a unicast HTTP session, the content of that session is between me and the webserver. No-one should be able to look at that without a warrant.

Looking at IP/layer 4 headers is ok because you're not seeing the "communication content" and there is no personally identifiable information except your IP address. To correlate an IP address with me is something only my ISP can do, so releasing the info to a third party seems ok...as long as they can't correlate the IP address to a name/person.

Jonathan