http://www.stanaphone.com/ (NO LONGER IN SERVICE since December 1, 2008.)

Free VOIP to/from PSTN service. Assigns numbers within various New York area codes.

Official client is a modified SJPhone soft phone.
Other SIP clients known to work include Cisco, Sipura, Grandstream, Atcom, X-Lite, SJPhone, etc.

All calls between StanaPhone users are free.
100 minutes per month free to 11 countries. Additional minutes can be purchased with a StanaCard.

Active user forum.

Sample Asterisk config for StanaPhone

---

VOIP Service Providers