A CCS Network  is defined in ANSI T1.118 as:

CCS Network: A set of signalling points (including STPs), using
out-of-band signalling, that are operated, administered, and
maintained by the operator of the network.

A "large" SS7 CCS network provider is defined in ANSI T1.118 as:

A large CCS network is a CCS network that provides signalling for more
than 75 signalling points (operated, administered, and maintained by
the operator of the network) in the first year of operation and at
least 150 signalling points (belonging to the network) by the end of
the first 5 years of operation. Also, it must have at least 6 network
elements providing STP functionality in the first year of operation,
and at least 12 network elements providing STP functionality by the
end of 5 years of operations.

My question is this:  What are the peering arrangements between large
SS7 CCS Network Providers.  In other words, when a subscriber from SBC
calls a subscriber on the Verizon network (assuming they are both
authorized by regulation to place the long distance call) does SBC pay
Verizon for use of it's SS7 network?

I have a pretty good idea how it works when a smaller service provider buys an
SS7 link from a larger provider.  They pay for the circuit and they
pay for SS7 messages, and they pay for enhanced services like CNAME. 
But how do the core SS7 network providers charge each other?