XDA-Developers Forum has a nice tutorial that shows you how to change the default system fonts on Windows Mobile 6 to that of any other Windows Vista, XP, Mac or custom font. You should also be able to change fonts displayed in the Start Menu, Soft Keys and the Settings Tab using this registry based hack. Before following this hack, make sure ClearType is enabled (from Start->Settings->Device->Screen->Cleartype) since some Vista fonts are meant for the same.
In this tutorial let us assume you want to install the controversial default Windows Vista font type “Segoe UI”.
1. Copy your font file (usually with the *.ttf extension) from the Fonts folder on your PC to the “/Windows/Fonts” folder on your mobile device. Be sure to note down the internal name of the font by double-clicking on the file in Explorer, in this case “Segoe UI”
2. Using your favorite registry editor (desktop based mobile registry editor, CeRegEditor, is handy), navigate to HKEY_LOCAL_MACHINE\System\GDI\SysFnt
3. Find the key named “Nm”. Replace its value (usually Tahoma) with the internal name of the font you want to replace , in this case “Segoe UI”
4. Repeat Step 3 for “HKLM\SYSTEM\GWE\Menu\Menufnt\Barfnt” and “Popfnt”
5. Finally change the value of “Tahoma” under HKEY_LOCAL_MAHINE\SYSTEM\GDI\FontAlias, to the name of the Font you want to replace i.e. “Segoe UI”
6. Soft Reset the device.
After the reset, you will notice that Segoe UI is the default font for the OS which renders more easily on your eye.



