When you war dial,at least back in the days of BBSes, you are scanning every phone number in a range (eg 555-555-xxxx) to find BBSes,fax machines,carriers, company dial-in computers, and more!
Person 1: Hey, do you want to war dial?
Person 2: Sure, I need some hacking BBSes!
To call someone an excessive number of times. This can also be used to describe text messages and instant messages
Jesus, she's called me 14 times already today. She won't stop war dialing me