Well I have been using VOIP for a while now and for the most part it has been very worth while, the only niggling problem has the the occasional degredation of voice quality. For 90% of calls it is as good if not better than PSTN, 5% are a bit choppy but Ok and clear up but the other 5% are just downright annoying and I can not hold a conversation.
Unfortunately when it goes wrong it really goes wrong and in most cases I can hear the other end perfectly, they can not hear me. Hanging up and trying again can help, rebooting the PC seems to clear it up. So by trial and error it seems to come down to the software phone I have been using, testing has shown that when it goes bad I can jump over to Skype and things are clear, same hardware and line just different software on my end.
This week I went out and purchased a brand new LinkSys SPA-3000 this is an Analogue Telephone Adapter or ATA, with this you plug in your broadband connection in one side and a normal phone in the other (the phone needs to be self powered so a cordless works really well) you can also plug in your normal telephone line in as well and have the benifit of using the one phone for both systems.
Configuration took about 15 minutes and then you have to set up the dial plans, that took about an hour to work out just what I needed but the guides over at the whirlpool forums were a great help
In the end I had it all ready so now I can make calls STD and international just by dialing the full number and the ATA checks the call and dials out using my VOIP carrier of choice. Local Brisbane calls get switched out over the PSTN network and I can receive calls on PSTN and VOIP on the same handset. Being a cordless means that I am no longer tied to my PC to make a VOIP call and the quality is even better. All major codecs are supported including G.729a and G.711 both U and A law so you can use the codec that is best for your situation.
Is it worth it? Well at $140 for the ATA if you are serious about VOIP then I would say yes! The original Engin voicebox is the older model the SPA-1000 and the new Voicebox 2 is the SPA-2000 you can buy either of these units and they also offer great quality as well but the new SPA-3000 has the ablity to run up to 5 VOIP carriers for outgoing so you can choose the route you wish.