System-Wide Font Replacement Comes To The iPhone, FinallyMonsta'd on December 31st, 2010
Those of you who rocked FontSwap on your iOS 3.x powered device have probably been looking for an app/tweak that allows you to swap fonts on your iOS 4.x device. This is where BytaFont comes in. BytaFont is a super easy-to-use Cydia application, which allows you to change your iPhone's [or other iDevice's] font. And we're not talking just the SpringBoard font, or your Notes.app font, we're talking full, system-wide, iOS font replacement and modification.
Installing new fonts for your iPhone is as simple as downloading them in Cydia, and activating those custom fonts is as simple as opening up the BytaFont app and activating them. By default, choosing or activating a new font will affect the font display on your entire iPhone, but if you'd like, you can tell BytaFont to only activate that custom font in certain apps or situations (pictured above).
You can find out more about BytaFont at the official blog here, or head on over to thank the cats at iPhoneRuler.net for developing and releasing this sweet tweak... for free. If you want to just jump straight in, hop on Cydia and search for 'BytaFont'.