Your phone must be rooted.
Open root explorer, navigate to /system/
Mount your System r/w and open the build.prop with a long press and choose "open in text editor"
Then scroll to the correct line, delete the "1" and change it to an "0".
Then save and exit and don't forget to reboot your phone.
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Dev of FormelsMIUI Mod on Nexus One
Dev of KelLMSKing MIUI Mod on Nexus S
Themes for HTC Hero, Nexus One, Incredible S a.s.o.