I have a single iPhone case I occasionally don specifically for use with a runner's holster, another with an extra built-in battery for traveling, but otherwise I've always kept my phones "naked". But recently a friend mentioned she has numerous cases for the sake of fashionably changing things up throughout the week (in addition to protecting her phone). Apparently this "closet of cases" isn't all uncommon...
Reset My Case is a newly launched subscription service offering iPhone owners the convenience of new inserts delivered every month for $5, allowing customization with a slide-in/slide-out design. The inserts are made of card stock with designs printed from three different categories: Illustrated, Patterned, and Typographic.
There's also the option to purchase inserts in bulk, in 5, 10, and 15 assortments if you're the impatient type. Currently the subscription service is available for both the iPhone 5/5S and iPhone 4/4S, with plans for other (presumably Android) devices "coming soon".
Of course, there's no need to subscribe to a service if you're up for a DIY solution, which is what Maegan Tintari of ....Love Maegan did using a cheap clear rubber case purchased from a mall kiosk. Realizing there was enough space between her phone and the clear case to customize to her heart's content, she first decorated her case using a real peacock feather, then some carefully traced/cut scrapbook paper, and a finally a favorite photograph, all for embellishing her iPhone in a style wholly reflecting her taste.
One great tip she shared: use pre-drawn outlines for the iPhone 4 or iPhone 5 devices as templates for printing out custom inserts. An additional recommendation I'd add: print out ink jet inserts using waterproof archival quality ink. If somehow some water or condensation gets into the case, these water resistant inks will unlikely ruin both case and phone with running ink.