An innocent question that has consumed my week.
I discovered voip-info.org and reviews of various VoIP (voice over IP) phones that are available now, and the rather impressive Asterisk open source PBX software.
This led to the discovery of broadvoice which is another VoIP to regular phone gateway service, that'll let you bring your own equipment (unlike my current provider vonage.)
I also learned about skype.com which unlike asterisk is closed source, but still free for PC to PC calling. Also Skype uses an IM style interface for dialing instead of the old enter a phone number. (Skype also apparently uses a higher quality compression algorithm than most phone service and transmits more of your voice than regular phone service.
Skype also has gateway services for either calling regular phones (SkypeOut) or receiving phone calls (SkypeIn).
The really impressive thing about SkypeIn is that getting a phone number is 30 EUR per year. Yep $40 gets you a phone number which can receive calls from all those 20th century phones for an entire year. Broadvoice's cheapest service is $5.95 per month, which includes 100 outbound minutes per month). Skype sells you credit in 10 EUR increments which are .017 EUR per minute to most of the US and Europe.
Though I read about a canadian who has me beat in The Limits of SpongeBob SquarePants, this guy has a zaurus with a GSM card, so he can switch it between being a cell phone and a VoIP phone depending on where he is.
Also since my girlfriend and I mostly communicate through IM i'm not really sure how much I need in the line of phone service, nor how many of my friends can I drag onto the VoIP bandwagon.
Though to make VoIP really easy for people requires some extra hardware to make their phones connect to the IP network, like oh, this widget or perhaps this phone.