Several years ago, when we started development of ITScriptNet's font support, one of the first things we noticed was that Windows CE and Windows Mobile devices have a different set of fonts than Windows on the desktop.  All versions of Windows since Windows 95 have included Arial and Time Roman, as far as I am aware.  However, enumerating the fonts on a Windows Mobile device shows a different story.

Instead of Arial and Times Roman, we get Tahoma and Courier.  Why is that?

I can't find any official information on this, but I believe I have a good idea of the reasoning.  First, let's start with Verdana, a font that is commonly used for Web design.  This font was specifically designed for readability in small sizes on screen.  You can read an interview with the designer here.

So why Tahoma and not Verdana for Windows Mobile?  Well, Tahoma is also a font designed for readability at small sizes on screen, but is a narrower font with slightly less space between characters.    I suspect this may be one reason.  With a 240 pixel wide screen, a narrow font saves valuable real estate.

There is also another reason that I suspect may be important.  In comparing the Wikipedia entries on Verdana

 and Tahoma, I discovered the mention of the Combining Characters Bug, and that Tahoma has better Unicode support.  Since Windows Mobile is entirely Unicode-based, it makes sense that a font with good Unicode support would have been chosen.

So, although I can't find any documentation to prove it, I believe that Tahoma was chosen for Windows Mobile because:

1. It is highly readable on screen and at small sizes
2. It has good Unicode support
3. It does not have the Combining Characters bug.