This might not be responded to because it is not clear exactly what you want to do...
Do the people you are calling have access to a computer?
Or... are you hoping to save money by making calls to people in other countries (on the telephone) using a computer on your side.
If you are asking the second question... there are a couple of companies that will offer this service.. I believe Skype is the biggest.
I haven't been convinced that these services are the best deal for making calls. When I call out of country (a couple of times a month), I find that international phone cards where you call a local number and then enter the number and a PIN are a cheap option with reasonable quality.
If the people on the other end have a internet connected computer, we set up a voice chat on any of several chat networks that support this. We have even set up video chats-- which are a bit flaky at times... but fun and usually quite usable..
This option is free (if you have two internet connected computers).