In the parent's description, it's not spoofing at all. They've purchased real american (local) phone numbers, and are routing calls through them through other means (like internet...). There's no telephone network level trickery or spoofing going on.
Not always. They will spoof legitimate numbers that they don't own. If you call them back you'll usually get some very confused person who just got a bunch of calls accusing them of making spam calls.
