For the first time, the nation's largest wireless provider is losing customers faster than it can replace them. It's a major milestone for Verizon, which on Thursday reported a net decline of 289,000 cellphone subscribers over the past four months. Even though Verizon usually loses some cellular customers every quarter, it has historically lured enough back to be able to report growth in that part of its business. But recent months have seen hundreds of thousands of customers defect to competitors such as T-Mobile and Sprint, analysts say. Things could have been even worse if Verizon hadn't suddenly reintroduced unlimited...