The second claim is not true. I can call with my SIP softphone worldwide (to the "normal" network) at good rates and with good quality. And yes, it already works behind NAT/Firewall without configuring/open the router. And yes, its OSS (kphone), you just have to connect to a SIP provider, which is free as long i don't call outside the SIP network. Im not aware of a German SIP provider where you have to pay for that, dunno how this is handled in other countries.