As far as Fiber or coper pairs/cable you can keep a private wan and still use the telcos. All you would have to do is use technology's like Frame Relay
Frame is cheap and good for data. ATM is a bit more expensive and requires a bit more knowledge on user side but is perfect for video, voice, and of course data. SMDS(Switched Multi Mega bit data service) is on the way out, but it can reach speeds up to DS3 (45 mbs). FDDI/TLS I am not too familar with. Many of our Government customers use this. It is an end to end fiber solution. Now we have up to 10 gig lines in this service. The beauty and apeal of this is there is no tapping this line. It is fiber. No one has yet figured out how to pull the signal off fiber without disrupting the transmission.
Last but not least is IP/VPN. This is the future and what the US DoD should do. You can bridge multiple standards across an IP/VPN network and be able to talk just fine. It is a global solution, it is cheap, it is secure, it will get better in time.
IP/virtual private network.