The truth is, the Alexander Technique is unique among bodymind disciplines.

It is like yoga in that it is a discipline that helps the student look at what he is doing or how he is doing an asana, but more than this, he is learning to become more aware of himself and to expand his awareness to include his environment, his sensing of himself standing and moving. It is not like yoga, because it is not a movement form. 

It is like massage in that the student is learning that his musculature has become tight and unresponsive in daily life, and he can recognize the discomfort, but it is not like massage in that he is learning a new skill and ability to recognize and change habits that are creating the tension.  So the difference is huge. 

The Alexander Technique is a gentle and specific process of learning to engage one's thinking process in order to maximize the comfort and ease for doing all of the daily activities of life.  By the time the person shows up at a massage office, there is most likely a significant amount of habitual tension accumulated.  Surprisingly, it is the most typical actions that we do, like sitting in front of a computer for long periods of time, driving, carrying grocieries, walking up and down stairs, that over time develop the long term habits that contribute to pain and poor posture, and even fatigue. 
Taking a yoga class is a great beginning, and a wonderful resource, as is massage, but we Alexander teachers are most excited for the person when he begins to make the connection that these insideous problems of collapsing while sitting, pulling down on himself while standing in line, tensing the joints while driving...all of these ordinary activities accumulate and lessen the chances of having ease and poise.

I was recently involved in a wellness day at my local library, and after awhile decided to visit the other booths at the fair.  We all had our brochures are were peddling our wares, so to speak, and it was the brochure at the massage table that most struck me.  This center boasted almost the same gains that I was saying in my brochure...less back pain, better posture, stress relief, feeling and looking better after studying...so I really got to thinking about the questions that potential clients ask.  These are important questions because we are always looking for context when considering trying something new. 

So my answer to the questions "Is it like yoga?  Is it like massage?" is the following.  In the Alexander Technique you are going to learn to become freer in body and mind because you are involved in an educational process that brings more wholistic connectedness to your intentions for doing something.  By learning to make better conscious choices, the "how" as opposed to the "what", you begin to discover that you have opportunities for moving and reacting to life's stimuli with less stress and strain.  No exercise form or theraputic model will do that for you.  You are learning to do something for yourself, and changing habits that are no longer useful.  Those habits fall away over time, and you become quite free, looking better, walking taller, having more grace, breathing better, and and enjoying life more fully in the moment.  (Almost) nothing can throw you off your course!

As you can see, I recommend finding an Alexander Teacher in your area!