What? Yes. AnyFont is a proper, available-in-the-App-Store iOS app that lets you install fonts system-wide, for use by any app that allows access to the full list of iOS system fonts. How does it manage this sandbox-skipping magic? Installation profiles.
Install the $2 app and you can use it to open any OpenType (OTF) or TrueType (TTF) fonts on your iPhone or iPad (the app is Universal, which is a nice touch considering that an iPhone-only app would have been sufficient). It works using the standard Open In… dialog, so you can mail fonts to yourself, or drop them into a folder in Dropbox.
Then, tap the font and it installs. This is done by creating a configuration profile and putting the font inside that, and therefore (waves hand to make it looks like he knows how it works) making it available to any app on your device.
These profiles are used for many things. For instance, the Eye-Fi app uses one to let you connect to the Mobi card over Wi-Fi without entering a password, and Testflight and Hockey apps use it to let you install beta apps from places other than the App Store.
It’s a hack, for sure, but a pretty clever one, and you can uninstall fonts easily enough just by deleting the profile. Ironically, this also brings back memories of the bad old days of font management on the Mac. Still, if you must, just must install Comic Sans on your iPad, now you can.