If you are not satisfied from the voice quality of the available VOIP utilities then try VoipOneClick. Every one want to make long distance calls at low rates but most of them compromises on voice quality but, this software gives you a good voice quality even on mobile networks 3G.
And what is the most surprising part of the program is you don’t have to perform any registration or configuration of personal data, you can directly start using it after the download. But, both parties should use the utility. There is also a paid per call function available which allows you to make calls with more secure privacy even to usual phone numbers.