I only see it mentioned on FreeType’s website, with no details:

“Some products which use FreeType for rendering fonts on screen or on paper, either exclusively or partially: [...] iOS, Apple's mobile operating system for iPhones and iPads”

http://www.freetype.org/

iOS (née iPones OS) never used subpixel rendering, and since the introduction of HiDPI it isn’t needed anymore either. I can imagine that using parts of Freetype instead of using the whole of OS X’s Quartz would’ve made the code for iOS more compact.

http://bjango.com/articles/subpixeltext/

Given that all of the iPhone models and many of the iPad models have HiDPI screens nowadays, I doubt Apple will be using Adobe’s extension, since it’s mostly a problem with low resolution displays.

There is a marked difference between letter shapes rendered with FreeType and with Quartz.

Judging by the letter shapes, I would say it's highly likely iOS uses the same renderer as OS X, at least for common fonts like Helvetica Neue.

However, I don't know if I've seen any CFF fonts. Perhaps this is where FreeType would come in?

Adobe’s solution is mostly interesting for OpenType/CFF and PostScript fonts. iOS’ system fonts are TrueType, so this would only come into play in websites, third party apps, and PDFs that use embedded fonts. Besides, iOS doesn’t use hinting embedded in fonts.

http://blogs.adobe.com/typblography/2010/12/the-benefits-of-...

http://blogs.adobe.com/typblography/2011/09/postscript-comes...

“There is a marked difference between letter shapes rendered with FreeType and with Quartz.”

Oh, definitely. FreeType has always looked like crap (to me) and iOS never did, so I don’t believe iOS’ font renderer is 100% FreeType.

From what I've experienced, I find iOS and Android font rendering is equal in quality, and Android uses freetype so I wouldn't be surprised at iOS using the same.