Sorry, but I really don't get the picture. Let me tell 
you about what a proxy is:
A proxy server has 2 main functions.
1 it blocks unwanted traffic through the internet, 
thereby eliminating unpaying customers, illegal 
traffic, etc. (It's not allways working, but you get 
the idea :))
2. It caches information requested by other users, 
thereby saving bandwidth, and delivering fast data to 
it's users.

I have never heard such a thing as an open proxy, and 
certainly not an anonymous ISP (Internet Service 
Provider). They earn their money on customers, and 
wouldn't deliver any service for free......But good 
luck searching the net. (is someone pulling your leg?)