I'm using FontSwap and I found a really nice old school Beastie Boys font (Ratcage) on beastiemania that I attempted to install using FontSwap. I duplicated the "Alba" directory for LockClock Font, dumped the .ttf in my dir, renamed properly, set permissions right but when I respring it just hangs. Luckily the network backend is still alive so I can go in SSH and dump it from the cache/font dir and replace it with default. As soon as that copy is done the phone springs back to life.
This is not the first time for me running into this, I feel like I have all my bases covered, my new font looks just like all the rest in FontSwap...
I believe installing a font requires more than dragging and dropping any ttf file and renaming it. There is a process you go through to make it iPhone-ready, otherwise, it will hang once you reboot. You have to use a program called Fontlab to convert the ttf file and there is a font-making guide I've seen at macthemes. Not sure if there's one on MMI but have a look around.