The federal law in 47 USC 227(e) says:
(1)In general
It shall be unlawful for any person within the United States, or any person outside the United States if the recipient is within the United States, in connection with any voice service or text messaging service, to cause any caller identification service to knowingly transmit misleading or inaccurate caller identification information with the intent to defraud, cause harm, or wrongfully obtain anything of value, unless such transmission is exempted pursuant to paragraph (3)(B).
In (3)(B) is a narrow carve-out for law enforcement and court orders.
The important point is that spoofing is illegal with fraudulent intent, OK with benign intent.
This is a very interesting conversation as there is a ongoing discussion on how to ban spoofed calls here in Italy.. Here operators must identify each customer and ensure that they are screening incoming numbers. Most do, but some do not and become sources of spoofed traffic. The biggest problem however comes from out of country originators that allow foreign call centers to use Italian numbers. Thus the calls come in from an international carrier. We are moving twords blocking incoming calls from international trunks containing Italian from numbers, something we see already in place for carriers in other EU countries such as France. Most operators here have been against stir/shaken as a means to resolve the problems. Brian