Looking closer it appears that this would probably fall under the stored communications act, since it relates to electronic messages not intercepted real time and no one has attempted to prove texts would fall under eavesdropping/wiretapping laws, presumably because they are covered under the SCA.

That being said, under 18 USC 2702 “Voluntary disclosure of customer communications or records” I think there’s actually a stronger argument under that law. You would either have to argue that ChatGPT is a provider or that they are an intended recipient, which goes back to my original point about all parties consenting to ChatGPT obtaining the content of their messages.