I've found a number of interesting-sounding papers on the topic of the momentum of light in a refractive medium. Frustratingly, I can't access them in their entirety. Amongst what I found are:
"The momentum of light in a refractive medium" , Peierls, two papers
http://rspa.royalsocietypublishing.o...1/475.abstract http://www.jstor.org/pss/79058 http://www.jstor.org/pss/79317
Also, a more recent http://prl.aps.org/abstract/PRL/v104/i7/e070401
(and a physicsworld.com article citing it that was .... not very well written.)
Peierls makes the interesting observation that it's not only light that caries the momentum when an electromagnetic wave travels through a medium - motion of the atoms in the medium (or of the medium itself in the continuum approximation) are also generated, in particular acoustic waves (which I assume could also considered to be phonons).
It'd be nice to see a full treatment of the problem that was accessible.
[add]http://www.opticsinfobase.org/aop/abstract.cfm?uri=aop-2-4-519 also looks interesting.