If you're always in range of a Wi-Fi access point, Skype may be the cheapest way to make calls this side of, well, anything. However, nobody but a road warrior with a laptop would really need a USB-powered screenless Skype phone.
The VTraveller hooks into your laptop via USB and has voicemail, LEDs, and personalized ringtones. You don't get an LCD display because this thing only costs $29, but you do get the privacy features of talking on a phone instead of using the built-in speakers and mic on your laptop. Kinda awkward when you're having Skype-phone-sex and Mark Wilson's listening in. Wait, did we say awkward? We meant totally awesome.