VoIP or Internet Telephony is a NGN-appliance and maybe one day will totally replace telephony over POTS. A couple of VoIP-protocols are available, e.g. SIP.

1. Internet connection
2. a VoIP account at some VoIP provider
3. VoIP hardware (e.g. a SIP telephone) or/and VoIP software on your PC

• you do not require a Router or OpenWrt to use VoIP!
• in case you have a router, and it's doing Network address translation, you have several possibilities to make your VoIP traverse your NAT:
  • voip.sipproxd
  • STUN solutions for STUN

The OpenWrt repository contain a couple of software packages, to enable you to not only make your VoIP work through your NAT, but also do "cool stuff" with it:

• voip.asterisk is a software PBX
• voip.kamailio / voip.OpenSER
• voip.OpenSIPS
• the packages sipp & sipsak

http://forum.openwrt.org/viewtopic.php?id=27103