When I was new to miles and points, one of the biggest deals was signing up for and switching long distance carriers. Then there were big mileage offers for cell phone service. Those dried up a bit with number portability, when a company acquired a customer the customer wasn’t really locked in past the end of their contract the way they had been so it wasn’t worth spending as much to acquire a customer.
A dozen years ago I earned 10,000 miles for signing up for Sprint service, Sprint had a cell tower on top of the building next to my office and I got a great signal even in the parking garage.
It’s possible to earn miles again for Sprint service. You can register your American AAdvantage number at Sprint stores.