Federal Communications Commission Chairman Julius Genachowski has announced his resignation from the Commission.

Among the achievements Genachowski himself claims for his tenure are a shift of universal service programs from voice support to broadband (Connect America Fund) as well as spectrum policies (incentive auctions, freeing up more spectrum, spectrum sharing concepts, 5 GHz for Wi-Fi use, TV white spaces) and network neutrality rules.

Blocking the AT&T purchase of T-Mobile (News - Alert) USA and the development of the National Broadband Plan are other achievements the FCC (News - Alert) would claim under the Genachowski chairmanship.

Those likely would be acknowledged now as the likely legacy of the Genachowski chairmanship. Of course, all eyes now turn to his replacement.

Names mentioned as potential replacements include Democratic FCC commissioners Mignon Clyburn and Jessica Rosenworcel; Catherine J.K. Sandoval, a member of the California Public Utilities Commission; Karen Kornbluh, the U.S. ambassador to the international Organization for Economic Cooperation and Development; Lawrence Strickling, head of the Commerce Department's National Telecommunications and Information Administration; and Washington, D.C., venture capitalist Tom Wheeler (News - Alert).

It always matters who the chairman is, since the FCC has a major say in shaping the direction U.S. communications businesses can take, or cannot take. On the other hand, the agenda is always shaped by what happened before.

One perspective is that, under Chairman Reed Hundt (News - Alert), the FCC maintained a policy of benign neutrality and non-regulation toward the infant consumer Internet.

Under Chairman Bill Kennard, the FCC encouraged the growth of VoIP.

Chairman Michael Powell pushed hard for the principles of net neutrality. Under Chairman Kevin Martin, a couple mega-mergers in telecom were approved and TV white spaces were made available for unlicensed use.

Among the biggest challenges that certainly will face the next chairman is the transition to IP, and the rules that will govern U.S. IP communications.