>> Not to mention the fact that the number
>> will no longer be valid, and the spoofers
>> will have to get a new number to fake.
Nope. They can make the caller id 555-555-5555 or any thing they want. It doesn't need to be valid number
I use the 555-0100 to 555-0199 block to call out to company cellphones. By saving something like "Sales" "Marketing!" "Cust Support!" "Server Room is 90F" as the name of each number we can know what the call is about.