When Microsoft recently agreed to buy 666,624 IPv4 addresses from bankrupt Nortel you might have asked, at least I did, how this was possible. No mechanism existed in the IP address allocation system for one owner to sell addresses to another.
But now there is, at least for ARIN, the American Registry for Internet Numbers, the authority for allocating addresses for North America and some surrounding territories. Maybe the policy has been there for a while, but ARIN won't say if it has been put to use before.
The policy is the Specified Transfer Listing Service (STLS)the Specified Transfer policy and was formally adopted in September, 2009. Through it, the owner of a block of addresses can return the block to ARIN, which will then allocate it to the other party. The receiving party has to qualify as needy by ARIN's standards, which are defined in their policies. The two parties can come to a private agreement about it, under which, presumably, money will change hands, but that's none of ARIN's business.
This policy is important because the IANA is out of IPv4 addresses and the Regional Internet Registries (of which ARIN is one) will run out eventually. At that point civilization will collapse, cannibalism will become rampant and the Cubs will win the World Series.
An effective private market in already-allocated IPv4 addresses will give us more time to get ready for IPv6. There are considerable wasteful allocations of IPv4 addresses. Companies with more than they need will have the incentive to sell in a private market when demand is such that the price is worth their while.
The increasing price of IPv4 addresses will have a beneficial effect on the overall situation, as it will make the migration to IPv6 more of a rational economic decision. You'll be able to get IPv4 addresses if you are willing to pay what it takes, but it might be worth the trouble of migrating since IPv6 addresses will be free and plentiful.
Hats off to ARIN for developing this policy, even if it's a bit too secretive. The prices are only available to those who have qualified as recipients, and information is important for a functioning market.