This page is outdated (except for the cartoon, which I find oddly prophetic considering that it was added around 2005, before the content migration...
Voice over IP, which these days is more SIP than H.323 and responsible for more unrealistic business plans than the whole internet bubble:

Resources:
- Asterisk - a full VoIP PABX solution in software.
- astmasters.net - a new focal point for the Mac OS X Asterisk community.
- There is also a very nice Mac OS X port with a Cocoa front-end and an active Mac mailing-list
- Jon's Phone Tool can also dial via Asterisk.
- Davi's Page on Free World Dialup
- You Don't Know Jack About VoIP - a nice historical overview
Providers:
- Free World Dialup
- StanaPhone - complete with fax support
- SIPGate
- Wengo
- PhoneSystems
