Sena Cases has introduced a number of cases for the upcoming iPhone 3G. The Elega Pouch is a slim case featuring a leather exterior, velvet lining, shock-absorbent padding, rigid inner layer for protection, a built-in belt clip, and holes for the iPhone’s speaker and microphone. It is available now in a variety of colors and sells for $40. The Ultra Slim Pouch is a slim sleeve-style case featuring a leather exterior, velvet lining, and openings…