It can't be used to send a message because all you can do is measure your particle. Even if doing so changes the state of the other particle far away (which isn't really what's happening, but that doesn't matter), all the other person at the end can do is measure their particle.

Neither of you can choose what the state of either particle is. You have no control, so there's no way to transmit information.

What you can do is agree in advance that you will both take certain actions based on the measured state of the particles. There's no way to be sure the person at the other end actually does so though.