Download or install a free VOIP application which is supported by your cell phone model. Google is the best place to search for VOIP applications for a particular cell phone model. Some common VOIP applications for cell phone contain Viber, NetTalk, Fring, Tango and Nimbuzz and not to forget Skype which is also a VOIP application and is supported by almost all modern cell phone models.
Enable Wi-Fi on your cell phone and let it search for a Wi-Fi hotspot. A list of in-range Wi-Fi hotspots will appear on your cell phone screen. Connect to a Wi-Fi network for which the Wi-Fi signal strength is fairly good. Connect to the Wi-Fi network which will connect your cell phone to the internet.
Now you have to login to the application you installed in the first step. Of course you will require a username and password for this. If you do not have an existing account for the VOIP application you installed, go to the official website of the vendor and create a free account. Use the login information to sign in to the VOIP application you choose earlier.
You are ready to make the VOIP call. Ideally, the call will be free if you are calling a person who is using the same application as you are and is signed in at that particular time. For instance, Skype to Skype calls are always free. However, you may have to pay a nominal charge if you plan to make a VOIP call to another cell number or a land lined number. See the vendor’s website for a detailed list of VOIP call rates.