Asterisk and PSTN

Good points about IP phones, but it's worth noting that many Asterisk resellers seem to install pure PSTN solutions not just VoIP - analogue or digital phones plus standard PSTN/ISDN into the telco. The reason is presumably that it's a drop-in replacement for a more expensive PBX and can still provide new features to these phones (e.g. ACD, smarter routing, etc), as well as to new IP phones.

Buying a lot of IP phones is pretty expensive compared to just replacing a PBX and its associated maintenance fees.