According to the National Institute of Standards and Technology, VoIP is not very secure nor is it ready for prime time use by the Federal Government here in the USA.
Citing concerns of h.323 vs. SIP and I guess MGCP too, plus concerns about VPN’s and NAT, the NIST folks seem to throw up more barriers to VoIP than any IT body has to date. That said, the company that best overcomes the issues is likely to win the lions share of Uncle Sam’s business.
My guess? Look to IBM as integrator, and Cisco as one of the key players. After that, factor in multiple number of the networks, possibly AT&T and MCI, with Level3 in some way also a part of the action.
Why those network and companies? No one ever gets fired for buying IBM or Cisco, plus IBM has a legacy of integreation behind them. Cisco is such a part of the plumbing they almost have to be a part of it. As far as the networks, MCI has been the government’s backbone for years. AT&T has the biggest IP network in the USA according to them, and Level3 is the player which has the best next generation network already in place, going to places where no others do, with more data centers and in many cases tons of miles of dark fiber.