I’ve been using VOIP at home now for 6 months - I have had a pretty good experience, so good in fact I can see why BT are switching everyone to effectively VOIP as part of 21CN (even as only from exchange point).

Kit I use is the Sipura SPA 3000 - which is owned by Linksys, and thus Cisco model.   Its very good, and surprisingly capable, although it is a properly tool for techies, in that the configuration of it is can be very complex.    This is linked to my DECT system, and BT line.   All BT calls come in, and can be answered on the DECT - however all outbound calls go via VOIP.   I’ve programmed it to act as a normal line would, and the missus (always important) has passed the technology  - she can often be heard talking about how she can call all her friends for free during the day.    Whats also nice, is if you are on a voip call, you can also switch onto the landline and back if you receive a call, similar to BT call waiting - it even can conference call.   Bear in mind if you get a SPA 3000 you need to regionalise it to UK settings, or it rings and has tones like an american phone (eaugh).  This requires a google search for the UK settings, and 10 mins to implement them all.

I’m using mine in combination with 3 SIP providers right now - Sipgate, Sipdiscount being the main ones -  and my BT line, and the savings in 6 months have paid for the kit many times over already, as I currently have free calls to the US, UK + many other countries for a very reasonable price (under £2/mo) and an additional incoming line.   £2 a month compared to the £45 phone bill (calls) shows the value.

Sipgate are really nice - they give **Free** incoming UK normal area code numbers, terminated to SIP.   This is good if you need a business line/additional line for the kids, and is a lot cheaper than the £11/mo another real line would cost.

In addition, I have found that the need for QoS is overstated/unnecessary in my case.   Even when a Bittorrent download is running, I find the voice quality is still perfect…   I’m using my normal ISP, and a  Netgear DG834GT for reference.    In most cases the quality is actually better than my landline now!

Next phase of my home plan is to implement a Asterix exchange on a Linux box on a mini-itx platform - this will sit under the desk, give voicemail/answering machine, and allow diversions from my landline to my mobile for key periods.   The main reason however, is this will allow several more VOIP lines to be added so I can have a proper office line, and I then will run proper VOIP hardware on my desk.

VOIP is good technology and it works right now, although implementing it is somewhat complex if you want the best call prices now (if you want it without this complexity/configurability, look up Vonage).    Doing what I am doing is also probably beyond most home users - although they can implement parts of it - what is nice for me is that I can pick the best rates for a particular country and program the SPA appropriately.