How is it possible for a text message I sent or even received to be forwarded to another person's phone?

Question

Invasion of privacy

Answer 1

I would assume it is possible because you lose all ownership of the message when you send it, leaving it up to the receiver to do with as they want.

Unless you expressly mention it I doubt it could be seen as an Invasion of Privacy...  

Answer 2

it is possible because you sent the message to them they can send it to any one they want with out your permisson and the same for you