I think that it would most usually mean 'I don't want to talk any more' - Most commonly because you have a dry mouth, or a sore throat from talking too much.

Basically yes, you are right. Depending on the context it could also mean: I have said everything I wanted to say I don't want to talk anymore There is nothing more to say It indicates that the person wants to finish the conversation as they believe that a) everything that needed to be said, has been said - or b) the conversation is not progressing anywhere, so the person does not see the point in in continuing the conversation. I hope this helps, Shaun.