Last-mile strategy for growing ISP

Hi all -

Please forgive my naivity, I've been in the IT industry
for several years but have made the transition to IT networks
(ISPs) very recently.

      I attended a networking conference recently and one
of the key note speakers (from a large ISP) mentioned in
passing the difficulties in delivering IP services to their
customers over their last mile infrastructure.

As one of the network managers for a growing ISP (our customer
being primarily government services) looking to provide more
IP services and get more government agencies on to our network,
what would be some of the challenges we might encounter in
delivering such services to current and new government bodies
over our last mile infrastructure ? What should be some of
our considerations ? What are some viable / cost-effective
strategies ? Where is the industry heading in terms of
last-mile offerings ? Are wireless technologies (with some of the
current security limitations) viable as a solution -- given the
confidential nature of governement data -- in the near
future ?

Any recommendations or thoughts would be most welcome.

Thank you for your time and patience.

J. H.