Looks like the North Koreans are moving ahead with their plans to launch a "satellite" atop a Taepo-dong 2 ballistic missile. This story describes something I've mentioned here before, a scenario in which the Japanese act to shoot down the missile, rather than the US.
The US and Japan have cooperated heavily in recent history to create an architecture of weapons, sensors and information that would enable forces from either nation to destroy ballistic missiles. Take a look at the two destroyers in the picture accompanying the story--you'll see the telltale signs of the SPY radar, heart and soul of the AEGIS Weapons System. What you can't see is the sophisticated network of communications systems that make up an information grid into which those destroyers plug, in order to gain fire control quality tracks.
I can see a scenario developing that goes something like this...depending on the trajectory of the missile, Japanese Maritime Self-Defense Forces (JMSDF) and US Navy forces are arrayed in such a manner as to give each nation's forces an engagement opportunity on the missile. JMSDF forces will be the primary shooters, with US in backup. The trajectory of the missile is very important, as it (and the position of the allied forces) will determine the number of engagement opportunities. The difficulty here is in the "kill assessment" process--that is, will there be sufficient time (and kinematics) to support a subsequent engagement if the initial shooter is unsuccessful? Ultimately, such a coordinated response might require interceptors from both nations to be in flight simultaneously, with the back up missiles command destructed in the event the primary missiles are successful.
You can be sure very smart people at the highest levels of the JMSDF and the US Navy are working hard to create a concept of operations (CONOPS) for this kind of thing...that is, if our governments have the will to carry it out.