[Asterisk-Users] DID reseller structures

[snacktime]

I'm curious about how a company goes about getting nationwide (US)
DID's for resale.  No I'm not wanting to be a reseller, just curious.

For example companies like XO or Level3.  Do they go out and cut deals
and/or exchange traffic with CLEC's/RBOC's in every region where they
1) need DID's, and 2) don't have a presence in that region themselves?

 And can you get a nationwide footprint by just going through one
CLEC?  For example does Level3 resell XO owned DID's and visa versa?

Chris