FontSwap Package format:
1. Package must be a folder with the name FontName.font
FontName is the custom font’s name that you’ve ported. .font at the end is essential.

2. Package must contain all fonts related to the category it belongs to.
Dialer Fonts: PhonepadTwo.ttf
LockClock Fonts: LockClock.ttf
Notes Fonts: MarkerFeltThin.ttf
System Fonts: Helvetica.ttf *and* HelveticaBold.ttf

3. Package must be placed in the correct folder in the packages directory
“/var/mobile/Library/FontSwap/Packages/Dialer Fonts”
“/var/mobile/Library/FontSwap/Packages/LockClock Fonts”
“/var/mobile/Library/FontSwap/Packages/Notes Fonts”
“/var/mobile/Library/FontSwap/Packages/System Fonts”

4. Fonts must be ported with correct metadata intact. Applying fonts with incorrect metadata will cause serious problems like app crashes or SWOD.
here’s how to port fonts http://blog.gauravgiri.com/2008/08/tutorial-port-fonts-to-iphone/
this issue will be resolved in future versions of FontSwap so that fonts with incorrect metadata will not be installed.

5. Package should contain an Info.plist file
this is not utilized in the beta release, but placing this file will help your package to be compatible with future releases of FontSwap
Sample:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>Author</key>
<string>Author Name</string>

<key>FontName</key>
<string>Custom Font Name</string>

<key>FontCategory</key>
<string>Category of Font</string>

<key>Description</key>
<string>Brief Description</string>

<key>URL</key>
<string>Author's Blog or Website</string>
</dict>
</plist>

6. Package should contain an image Preview.png with a preview of the custom font.
this too is not utilized in the beta release, but placing this file will help your package to be compatible with future releases of FontSwap.
Image dimensions must be 36px by 260px. It must show the Custom Font name in the font itself. Text size must be 24px. Text color must be black [#000000].

I know these are some strict rules but they will ensure that packages are uniform in appearance and easy on the eyes of the end-users.