Sugestions & Pointers for a complex configuration?

I have a client that over the years has set up a multiple location
network which for the most part does what it is supposed to do.
Unfortunately, due to ISP or Telco issues there have been times when
one location and been down for a while (usually 4-24 hours). I have
been asked to make a proposal addressing network changes that would
provide redundancy and therefore keep ALL their locations up and
runninging. Here are more details about the sites:

They have a main office with a T1 line. They have four remote offices
each with an ADSL line, a DSL modem and ethernet routers. Each router
maintains a VPN to the main office. 100% of their branch traffic goes
through the VPN to the main office including their Internet access
which is then routed through the main T1 router to control Internet
access. So far - works great!

As this is a financial institution the uptime at their branches is
paramount. Occasionally they have experienced drops with the ADSL
service in one or more branches which literally closes the branch.
They are exploring failsafe alternatives for all of these and future
connections. I personally have tried to come up with alternatives but
cannot come up with a viable solutions that will continue to maintain
the VPN links and even trying to use V.9x modems I cannot determine
how so much IP related services could be continued under these
circumstances. I've read about some devices out there that will
literally bridge disparate circuits into one so they will accommodate
such support but I do not know if and how they can interwork. As each
location operates under its own subnet, each device operates with its
own IP and the VPN's are dependent on specific IP's, how can one
configuration a solution?

I'm not asking for anyone to simply present a plan (although that
would be nice) but more to respond with recommendations as to what
might be or could be done to accommodate this requirement.

Hopefully this networking usenet group will have qualified readers who
will know the answers.

Thanks a million in advance for ANY advice & recommendations.

Bob

Can someone at Netopia drawing upon their vast knowledge of
internetworking please provide some recommendations and/or suggestions
as to how this can be accomplished? Even if it is something that
cannot be handled with Netopia equipment exclusively, do you know of
any other device that might provide this type of service?