Caller-ID spoof and voicemail
It’s easy to spoof caller-ID with some VoIP systems. There are a few Websites that specifically allow it. It’s a little harder, but geekier, to spoof or overflow caller-ID with a simple Bell 212A modem: it’s transmitted with that tech between the first and second rings of the phone. (Since most people have caller-ID these days, many telcos don’t play you the first ring. Since we don’t have caller-ID, we often get accused of answering the phone before it rings.) (Of course, the rings you hear on the calling side aren’t necessarily the rings heard on the other end, but …)
Apparently AT&T allows immediate access to voicemail on the basis of caller-ID.
Apparently, with Android phones, it’s also gotten even easier to spoof caller-ID.