There has been so much written about the retail/consumer side of VOIP (Has Vonage received more fawning coverage than any start-up since the height of the dot-com days?) that some parts of the emerging market have literally been ignored.
With this in mind, I ran across an interesting article in the Denver Post looking at how the growth of Internet telephony may help Level 3 and Qwest, which provide backbone telecom services. Both companies have suffered since the telecom blow-out but they do have extensive, state-of-the-art fiber networks that are starving for traffic. As VOIP starts to become more widespread, many service providers (cablecos, telcos) will need to access high-speed networks to build out their businesses. This could - and I emphasize could - help wholesalers such as Level 3 and Qwest.
The big unknown is competition within the industry. While some wholesalers have gone out of business, many of those that suffered during the telecom meltdown went through bankruptcy protection and emerged as leaner operations with little or no debt. A good example is 360 Networks Inc, which shed tons of debt and has gone on a mini-acquisition spree. This means there is still plenty of competition for IP-based business such as VOIP so it's not like prices for network access are going to surge or margins will miraculously improve.
While the Denver Post quotes an analyst who describes the wholesalers as "arms merchants", it is important to point out there are still many merchants in the mall so competition remains fierce.