[How To] Change System Font On iOS With BytaFont
The popular choice for changing fonts on the iPhone, FontSwap, unfortunately doesn't work on iOS 4.0+. Thankfully, we have a solution for you. BytaFont, available in Cydia for free, is the answer. Unlike FontSwap, BytaFont has been updated to use .ttc fonts (used in iOS4+) instead of .ttf fonts (used in firmwares below 4.0)
Once you install BytaFont from Cydia the first thing you'll need to do is download some fonts! Go into Cydia and look under the "Sections" tab. There should be a section entitled "Fonts" Go into that and find a font you like.
NOTE: In order to work the font description must say "Font Package to use with BytaFont". (Won't work if it says "to use with iFile")