There are many different types of Softphone. Before choosing which type of softphone you want to use, you need to decide on what VOIP service provider you are going to use. This depends on how much you are prepared to pay a month (if anything), and the quality of service which you would like. It also depends on how many phone calls you are going to want to make outside of the VOIP system (such as to normal standard telephone lines), the country in which you live in and the countries in which you want to be able to make calls to.
Softphone software is essentially a new way to make phone calls using your computer and or a device that is connected through the Internet. Some people refer to this service as Voice Over Internet Protocol or VOIP. This software is so powerful and flexible that it literally replaces the need for a traditional phone service supplied by companies like Comcast and AT&T.