This HOWTO talks about how to change the default fonts in Android mobile without any font management tool. The system fonts are available in /system/fonts directory. DroidSans.ttf is the main font used in most of the applications. Overwriting the fonts in this directory with your fonts will change the fonts in the Android mobile.
This involves two steps. One is to get the /system/fonts directory in read-write mode and another one is transferring your fonts to /system/fonts directory.
1. Make /system/fonts with read-write permission. Follow my previous post of Mounting /system partition in read-write mode in Android to get it done.
2. Backup the existing fonts and copy the new fonts using adb tool. Here # is the adb root prompt.
# mv /system/fonts/DroidSans.ttf /system/fonts/DroidSans_org.ttf
Repeat the above command for the fonts you are going to overwrite as a backup.
C:\android-sdk-windows-1.1_r1\tools>adb push c:\downloads\fonts\myfont.ttf /system/fonts/DroidSans.ttf
1145 KB/s (0 bytes in 73292.000s)
The above command will copy the new fonts. Repeat this command for all the fonts you want to overwrite.
Once your mobile rebooted, you can see your shining new fonts.
WARNING: Default font is tailor made for Android mobile to fit perfectly with all the controls and screen. There is a chance of imperfectness in your font for Android. In this case, you can revert back any time by following the above process.