problem with sass media queries + variables

Gemfile

source :rubygems

gem 'fssm'
gem 'sass', git: 'git://github.com/nex3/sass.git', branch: 'master'

Gemfile.lock

GIT
  remote: git://github.com/nex3/sass.git
  revision: a6a80a8a594d9a1f904b931ff4facf88bc4908b4
  branch: master
  specs:
    sass (3.2.0.alpha.0)

GEM
  remote: http://rubygems.org/
  specs:
    fssm (0.2.7)

PLATFORMS
  ruby

DEPENDENCIES
  fssm
  sass!

gistfile1.sh

bundle exec sass --watch style.sass:style.css

style.css

body {
  background-color: #eeeeee; }

.page {
  width: 920px;
  background-color: white; }
  @media screen and (max-width: 320px) {
    .page {
      width: 100%; } }
  @media screen and (max-width: $px) {
    .page {
      width: 500px; } }

style.sass

=respond-to($media)
  @if $media == phone
    @media screen and (max-width: 320px)
      @content
  @if $media == tablet
    @media screen and (max-width: 768px)
      @content

=respond-max($px)
  @media screen and (max-width: $px)
    @content

body
  background-color: #eee

.page
  width: 920px
  background-color: #fff

  +respond-to(phone)
    width: 100%

  +respond-max(768px)
    width: 500px

Oops, I didn't read that pull request closely enough. That wasn't merged in at all, but @chriseppstein says an implementation is in the works.