Last year, a spammer spoofed with my business phone number as their caller ID. Mid-day, I start getting phone calls from people yelling at me to stop calling them, stop harassing them. Every 2-3 minutes, someone new and angry. After about 3 hours I had figured out what had happened and got ahold of my carrier and had them change my phone number.
I don't know enough about SS7 to understand if this is feasible, but it is clearly time for a call back based system. Millions of people signed up for the do not call registry. I am sure millions would sign up for a system where incoming calls trigger a call back. If your out bound call system doesn't support call back, don't worry because nobody wants to talk to anyone hiding behind the cloak of invisibility.
I just don't answer my phone anymore unless I recognize the incoming number. And caller ID is trivially easy to spoof. Thankfully nobody spoofs any of the numbers of my top 50 contacts.