Two solutions have been considered for Ubuntu Touch: Pocket Sphinx and Julius. However Pocket Sphinx seems to be the long term choice for Ubuntu.
We built the voice feature around two different Open Source voice
engines: Pocket Sphinx and Julius. While we started with Pocket Sphinx
we weren't entirely happy with it's performance, and found Julius to
start faster and provide better results. Unfortunately Julius is
licensed with the 4-clause BSD license, putting it in multiverse and
making it so that we can't link to it in the Ubuntu archive version of
HUD. We're looking at ways to make it so that people who do want to
install it from multiverse can easily use Julius, but what we'd really
like is to make the Pocket Sphinx support really great. It's something
we'd love help with. We're not voice experts, but some of you might
be, let's make the distributable free software solution the best
Source : http://gould.cx/ted/blog/Introducing_HUD_2.0
CMU Sphinx is an open-source project that can also be used on the Desktop, Julius too.
On the long term Ubuntu Touch and Ubuntu for Desktop will be the same OS, so the answer to question like "can it be used on Desktop too ?" should hopefully be more and more positive.