Last I saw you could get spire/spite on 5.0.1 & 5.1. Look in the siri forum on this site. To be fair I would stay away from installing un less you know for sure that a siri/spire 100 percent works and un-installs properly. When I installed spite, it didn't work very well and slowed my phone down. So I un-installed and it messed my phone up big time. Therefore having to do a restore on my phone, which I have never had to do in a year.
If you really want this, I suggest you re search very hard and when you find something good, look at its feedback. Otherwise mate, I would get a 4S or go without.
Sorry to put a downer on it, but that?s just my experience.