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try this
Settings > Applications > manage applications **
Hit the menu key select Filter, Select all
> Scroll down to voice search, and force stop.
not sure if that will work or not...
nup dun work...
try rooting the phone and uninstalling..

I had uninstalled voice commands as there is no other way to disable it. I used Titanium Backup to freeze it but it continued to run in background and used 30+ mb memory.
You can use systemapp remover to backup and then uninstall vsuit.apk. Note that once uninstalled there will be endless force close until the phone is rebooted.how can you uninstall voice dialer? i have a rootted phone