Is it possible to subscribe to a newsletter without first having to register? I am using the Simplenews module, but from what I've been able to conclude, is not possible to subscribe to a newsletter without first having to register.  Is that correct?

Is there a different newsletter module which will enable me to do this: offer a newsletter subscription to users without having to first become a registered user?
It is supposed to be possible, but the anonymous user is still required to confirm their email address. Check this issue in the Simplenews issue queue.