Situation: Derek Hale wants to go on a date with Stiles Stilinski.
Problem: Derek Hale has no way to communicate with Stiles Stilinski other than showing up in his bedroom.
Solution: Derek Hale needs a cell phone.
In some ways (very few), Derek was lucky. When his family had died (unlucky), they had left behind money (lucky). He had a car (lucky), even if he didn't really have a house (unlucky). He hadn't ever thought about maybe needing a phone. He hadn't needed to communicate with anyone. He could always show up in Scott's room if he had to. Or, more importantly right now, Stiles's. Except somehow the 3a.m.-room-appearance didn't seem like the right way to plan a date. So he needed a phone.
Fortunately, there was an Apple store not far from Beacon Hills. Derek had never cared much about computers or iPods or whatever, but he had a vague sense that an iPhone was a decent phone. So early Saturday morning he drove out to it and, with the assistance of an "associate" at the store, picked out a phone.
He hadn't realized how expensive they were, but he shrugged it off. It wasn't like he had any real regular expenses. He was set for life, financially, provided he kept living in a burned-out shell of a house with no electricity or hot water. So maybe he should put a little more thought into his finances. That could come later. Right now the only things he was paying for regularly were gas and, now, a phone. And food, sometimes, when he felt like it. Like tonight with Stiles.