I'm a great advocate of Skype (if you use the free Skype to Skype calls, of which more later).
I have used it off a pc with headphones and mike and that is fine 99% of the time. Also have a dedicated router (in the basement) plugged into my wireless router at home, which gives me a cordless skype phone at home. The model I use can also take a landline, so it doubles as a regular phone. Signal quality is very good up to the ground floor, then starts to drop a little as I wend my weary way upwards, but it is still not too bad.
My son and daughter in law use a mobile phone £15 per month (UK only I think), and with that sub they get Skype 24/7 on their mobile. Thus, with me being on line 24/7 with my wireless and them the same on their mobiles, there is never a moment when we cannot be in touch.
For Skype to landlines or mobiles, check out their rates (what they call SkypeOut). While cheaper than most telephony service providers, they are still quite pricey. For such calls, I use dedicated VOIP suppliers (VOIPcheap, VOIPwise, VOIPbuster - all sister companies from the same stable). Sound quality is as good as Skype, and they are much cheaper with a lot of free destinations.
Hope this helps.