taken from this old post, it works
How to Root?
To install busybox on a firmware on the phone, there are a few ways. Easiest is to either use the rooted recovery v3 image or a rooted kernel.
If using the recovery, you'll need to boot up in recovery mode and connect your phone to your computer. For rooted kernel, just connect the phone when it's running normally and make sure adb is enabled in settings.
1. Run "adb remount"
2. Next push busybox with "adb push busybox /system/bin/busybox"
3. Create the symlinks with "adb shell /system/bin/busybox --install -s /system/bin" (you can skip this part if you do not foresee using the rest of the commands that busybox provides)
4. Modify cp's symlink to allow file managers to copy files "adb shell rm /system/bin/cp"
"adb shell ln -s /system/bin/busybox /system/bin/cp"