busy signal

I have been trying to call my parents all afternoon. I keep getting the busy signal. The first time I called, it totally threw my off-guard because I don't think I have heard that noise in years! I'm guessing that they took the phone off the hook for some reason because both of their cell phones are going straight to voice-mail too. Heaven forbid they aren't accessible to me 24 hours a day, 7 days a week. But still. That stupid busy signal is driving me crazy!