The latest packaged sources and official binaries are always available on our SourceForge project page.
(An old) GemRB is available through the Android Market. Check the project page for fresher builds also between releases.
A jail-broken device is required. Find the package and instructions on the iOS installation page.
git clone git://github.com/gemrb/gemrb.git
git clone git@github.com:gemrb/gemrb.git