AT&T is not the only GSP, but AT&T is one of the few telecommunications companies that have wiring spanning the globe.
Globaly their are about 20 true "GSPs"
GSP's are simply large scale telephone companies. They have their own routes for communications across the country, continent, globe. Whether its land line copper,fiber backbones, oceanic cabling. or cross continent satelite, they have a means to get your network packets from one place to another.
Most ISP's will have atleast two GSP's, the "Main" account and the backup. The billing cycle on these types of account can be based on bandwidth usage or could be a flat rate for a certain sized pipe. Usually, in an ISP, your main "pipe" is a flat rate and your backup is a per bandwidth charge. So while your not using your backup the fee is nominal.
The lines between ISP and GSP are getting vague. You need a boat load of money to setup a true ISP and from what I have seen lately, most ISPs contract out their actual server farm and bandwidth provisioning.
Their are tons of server farm companies out their and a lot of them have the money, size and need to actually be a ISP and have multiple GSP connections as backup and alternate GSP's for connections to different continents. So in theory you can setup an ISP in your office and never need to buy any hardware.
But I'm geting off the subject.
The internet itself is not owned in any way shape or form by the government. In essence the Internet is an interconnection of different companies telecommunications networks. They all agree to pass packets back and forth to each other to allow "commerce" to occur between competing Telecommunication networks. But their is really no rules on how to act.
Hence the big fiasco with Vonage and Verizon and the process of prioritizing packets for VoIP phone calls for your users.
Is the internet free? Sure.
If you have about 750 million to buy the hardware, lease the satelite bandwidth, or just launch your own!
Then you too can become a GSP!