I initially thought to disable the port, but didn't see where to do an individual port. But I'll look more for it.
More info since my original post: According to the on-site guy, if you're near the called extension, you will see X calling, where X is the name I've assigned. If you answer, you hear a high pitched tone, not a modem or fax tone. If you don't answer, it says there is a voicemail. But there never is a voice message left.

Jim