Talqer

Google Talk is  simple and easy to use. It is an open standard and the source code is freely available. And the voice quality is acceptable but it is does not include the ability to call people who are not online.
Talqer (pronounced Talker) integrated with Google Talk to allow users to make phone calls to normal telephones anywhere in the world. Talqer offered:

* Choice: You choose whether you want to integrate Talqer together with Google Talk or use it as a stand alone application

* Quality: Talqer was based on open industry standards and offers very high voice quality

* Convenience: Talqer added three buttons to the Google Talk user interface to allow you to call normal telephone lines from inside Google Talk

* Affordable: Talqer offered affordable rates: every single Talqer rate was lower than Skype at that time. Calls to 22 countries cost only 1.5¢ per minute: a 33% savings when compared with Skype for US callers and a 53% savings for European customers (no VAT). Calls to another 8 countries at just 2¢ per minute.