Pistol-whipping is retro. For fashion-forward abuse, it's cell phone-whipping. I've seen two of these in the last month. One was a young teen who was phone-whipped by her mom. Left a lot of bruises, some abrasions, no lacerations.
Think about it. A cell phone is solid, fits well in the hand. Cell phones are designed and manufactured with the expectation they'll fall on the floor occasionally, and to the phone, hitting the floor is no different than hitting someone's zygomatic arch. F=ma, so high technology phones work better: technology = weight. If you're looking for the best instrument for slapping up that kid you caught in the wrong neighborhood, or teaching a lesson to the scumbag dealer who sold you cocaine cut with levamisole, the newer smart phones, like the HTC EVO 4G or the Motorola Droid (both weigh in at 6 oz.) will prove most effective. Be prepared to pay up for a quality weapon.
One of the best things about a cell phone is its invisibility. Walk down the street swinging a gun -- whoa, way too much attention, unless you're in Helmand Province, or partying with these guys. But walk down a street carrying a cell phone? Yeah, you and the rest of the world. A melee weapon in plain view -- and no one cares.
I foresee a big future for phone-whipping.