Get the free Glyphs Viewer app, and see how your font performs on an iOS screen, including Retina displays.
First, download the free Preview Server Plugin for Glyphs. Once it is downloaded, simply double click it to install it. Restart Glyphs. Update: the plugin is not needed anymore, the functionality is built directly into Glyphs. Simply make sure you have the latest version of Glyphs, and Glyphs > Preferences > Sharing > Enable External Preview is on.
Then, take out your iOS device, and download the free Glyphs Viewer onto your iPhone, iPod touch, or iPad.
Your font on iOS
To use it, simply make sure that both your Mac and your iOS device are in the same network. Glyphs Viewer will list all Macs in its vicinity which run a copy of Glyphs equipped with the Preview Server plugin. Once you select your Mac in the menu, the contents of the frontmost Preview tab will be replicated on your iOS screen. Cool.
To get back to the main menu, tap and hold the screen for a second until the Services button appears, and then, tap Services.
Now you can see what your font looks like on a Retina screen. You can zoom in and out very far, which is great for testing your font in small sizes. And you can lock the screen orientation and edit the kerning upside-down.
Update 2014-10-06: Removed the plugin link, added tap-and-hold instructions.