This problem appears because the virtual keyboard is not adjustable to screen size. So on a small screen with a high resolution the keyboard is very small (e.g. HTC Diamond). You in preferences the screen resolution. The default is set to small but if you set it on medium or large the virtual keyboard will be bigger at next login. By modifying the font size all text from every screen will be changed so this may not be a great solution for all handsets.
A note here: not all font sizes are available for every device. So if a device does not support a greater font size then a message will be displayed when trying to save the changes made to Preferences, saying:
This problem appears because the virtual keyboard is not adjustable to screen size. So on a small screen with a high resolution the keyboard is very small (e.g. HTC Diamond). You in preferences the screen resolution. The default is set to small but