It looks like there a few working solutions for using custom true type fonts (ttf) on the iPhone, most notably Can I embed a custom font in an iPhone application? However,
With regards to the first answer - the solution is correct (i.e. just convert the font over to TTF) but the software suggested is a super hassle to compile and install. Instead I just did a quick google search and used this instead: http://www.freefontconverter.com/ and that worked perfectly.
(Make sure to add the font to your info.plist file as well)