This is supported by iOS 3.2 and later. Straight from the document describing what's new in iPhone OS 3.2:
Individual Font Support
Applications that want to use custom fonts can now do so by include the UIAppFonts key in their Info.plist file and registering those fonts with the system. An array of strings indicating the font files in the application's bundle make up the value of this key. The system loads the requested fonts and makes them available to the programme when it detects the key.
You can utilise your custom fonts in IB or programmatically once the fonts have been configured in the Info.plist.
On the Apple Developer Forums, the following discussion is ongoing:
And, now a
good and straightforward three-step explanation for achieving this (broken link removed)
Xcode can be used as a resource to add your project's own font files.
Your Info.plist file should now have the UIAppFonts key.
Make this key a collection.
Enter the complete name of each font file you have (including the extension) as an entry in the UIAppFonts array.
To get the custom font to use with your UILabels and UITextViews, etc., you can now just call [UIFont fontWithName:@"CustomFontName" size:12] in your application.
Be sure the typefaces are included in your Copy Bundle Resources as well.