‘Google Now’ (google’s version of siri) has been ported to ICS. The developer that ported it, had to disable the voice recognition because it caused issues. You can still type stuff in to make it work though. Unfortunately, you have to uninstall the google search apk in /system/app (which requires root). If you’re willing to do that, then check out the original XDA thread below. Remember to read the whole thread before attempting.