ISDN... before it was too expensive, now you can't get it anymore. VoIP with G.722 is wonderful when it works (you can't just call everybody with it, because b

ISDN... before it was too expensive, now you can't get it anymore. VoIP with G.722 is wonderful when it works (you can't just call everybody with it, because both parties must support it). G.711 (A-law or µ-law depending on which continent you are) also works perfectly and gives the same quality of a regular landline. But in all cases the IP transport behind should work well, with very low jitter and not too much latency.