A friend of mine who is currently an inactive Army reservist forwarded me some memos he received regarding future mobilizations -- memos that indicate that we are not far from some kind of conscription in the next few years. According to my friend, recruiters are telling inactive reservists that they're going to be called up one way or another eventually, so they might as well sign up now and get into non-Iraq-deploying units while they still can. There's also a "warning order" -- i.e., a heads-up -- from the Army's personnel command that talks about the involuntary transfer of inactive reservists to the active reserves, and thus into units that are on deck for the next few Iraq rotations.
My understanding of how reserve call-ups work is imperfect, but if memory serves, the inactive reservists -- known as the Individual Ready Reserve -- are people who have already fulfilled their term of enlistment but can be called up as individuals if the military needs their particular skills or specialty badly enough. In other words, after a couple of years of dipping into the main reserves -- essentially chewing through them to sustain post-9/11 deployments, the Afghanistan occupation, and then the Iraq invasion -- we're now dipping into the inactive reserves. And if we still need more manpower after that -- well, then we start drafting.
http://www.prospect.org/weblog/archives/2004/05/index.html#003014