Imternetcalls is in beta and is free - http://www.internetcalls.com/en/index.html - I have been using it to call landlines around the world (and NZ) for the last few days. Yes you can call from PC to landline for free to certain countries including NZ, UK, USA, Australia and much of asia.
Big problem however is the 1 - 2 second lag those on the landline suffer. The only work-around seems to be telling the landline user to take the earpiece away from their ear while they talk. Otherwise quality is usually 6 to 7/10 and you don't have to have credit to call. Never had a call dropped due to time limits yet and have had calls last up to 15 mins to the USA and UK.
Might not be around long but if someone can find a way to solve the lag I'd love to know about it.