I don't think what you are after will be as feasible as it sounds like
you're used to in Europe.
In the US, there are _many_ different telephone companies each servicing a
certain area, and they each have different policies and procedures on
whether they will offer wholesale DSL in a given market. For this type of
wholesale access, you will need to make arrangements with each operator in
the area you want access to.
I will tell you that the usage of IP/L2TP as a delivery mechanism is not as
pervasive as I often hear about in other countries. In most cases, I've
found telephone companies still require you to have an in-market ATM circuit
to accept the handoff via PVC(s). This can get expensive, quickly, if
you're trying to aggregate connections to a single POP in NYC that are not
close to NYC, as you need to back haul that ATM circuit to each respective
market.
Additionally, FCC ruling some years back made it so the telephone companies
no longer must make available wholesale access to their DSL/broadband
networks, and as a result some no longer offer access to independent
operators. Those on your list of potential operators that do continue to do
so have had a policy of not offering new products/services to wholesale DSL
customers since this ruling, which I guess is most likely for "business"
reasons and perceived competitive threats to their own local broadband
offerings. The long term availability of these services is in doubt as
ADSL1 fades away. (Examples include: Qwest: No access to ADSL2
network/speeds, VDSL network/speeds. Lack/loss of wholesale access to DSL
in markets not supported by ADSL1 or converted away from ADSL1. Verizon:
No access to FIOS/Fiber-based services. Inability to get copper based ADSL
services at a location converted to fiber.)
Some, such as Verizon, also refuse to offer their wholesale solution to
people not using it for resale (IE: enterprise customers), regardless of
line quantities.
If you wish to proceed, here are links to the appropriate provider
information pages which detail their product offers and architectures:
Qwest: http://www.qwest.com/wholesale/pcat/hsihostservice.html
Verizon: https://www22.verizon.com/dslmembersonly/contents.jsp?show=aboutdsl
ATT: Varies by market, but you can find your links here:
http://www.business.att.com/wholesale/Family/ip-solutions-wholesale/dsl-transport-service-wholesale/
You may find in many cases, that contracting with a local/smaller ISP in
each market who has an existing wholesale arrangement with your desired
carrier in place, and asking them to deliver the services over L2TP, may be
the best solution for smaller quantities of connections.
Or seriously consider a VPN solution if it's more appropriate for what you
are doing.