The Callet's Callet for iPhone 4 ($20) isn't the first case we've seen that's designed to include wallet functionality, and it's not the best, but this silicone case may work for times when you want one less thing to occupy space in your pocket or bag. Callet's soft design allows it to easily wrap around the body of the phone; this means it can be pulled off without much force as well. Cutouts allow for access to all of the ports and buttons, and…