Last month I reviewed the iCache Geode, an iPhone case that replaces all of the cards in your current wallet with a reprogrammable one that morphs into any card you want. If that's a little too extreme for your taste I've got something a little more analog that might fit the bill.
Enter The Little Black Book ($59.99) from Twelve South. It's a wallet-type case for the iPhone 4/4S that includes three slots for your driver's license and a couple of credit cards. And like their amazing case for the iPad, BookBook for iPhone (as it's called) looks exactly like a leatherbound book.
BookBook is the perfect summer accessory because it allows you to consolidate two things you carry every day -- your iPhone and your wallet -- into one. It has just enough room for your driver's license and two credit cards and a slim pocket to stow a few business cards and an emergency $50 bill. I moved to a small wallet years ago and in the age of PayPal and debit cards I find myself using cash less and less these days.
My only complaint is that it doesn't have a hole on the back for a camera, so you need to pull the red tab at the top and take your iPhone out of the case to snap a photo. Also, it's also a little difficult to text in portrait mode at first, but I got used to that pretty quickly. BookBook for iPhone is easiest to use in landscape mode and it's annoying when iOS apps don't support landscape keyboards.
I've been using BookBook for iPhone for a couple of weeks and it's a high quality piece of kit that's extremely well-made. It actually looks better with age because the leather gets a great looking aged/weathered look. If you're looking to slim down your wallet/iPhone combo, give BookBook a spin. It's available in black (pictured) and brown from the Twelve South website.