pretty easy to use all you need is to download an app called Whatscall, I came across this app on playstore when I tested it,it worked just Fine and I would recommend you to use it too
★ Enjoy Calls that are Truly FREE!
Sick of phone bills? Say goodbye to them by using WhatsCall now. Call home and abroad with no extra charges. There are more than 200,000 people using it! Every user can get 2,000+ free call credits each day, that’s 30+ mins free time of calling home!!!
★ Unlimited FREE Call Credits
We have plenty of different offers on WhatsCall, just complete these simple offers and earn call credits to call non-WhatsCall users for FREE! You can receive up to 30 mins calling time each day easily by clicking ads, watching videos and inviting friends.
★WhatsCall to WhatsCall is Credit-Free
Calling online WhatsCall user is CREDIT-FREE. Invite friends to use WhatsCall and enjoy high quality online calling with them for free using Wi-Fi. Besides, you can call any mobile/landline numbers in more than 230 countries with free calling credits.
★Leave a Lively Video Message
Say goodbye to the traditional voice mail and indulge your friends with video messaging! If your friends are unable to answer your calls, you can leave a lively Video Message to let them watch what you have to say, and give a better picture on the importance of your message!!
★ High Quality Voice Calls
In conjunction with the world’s leading companies, powered by advanced voice coding and decoding technology, WhatsCall takes pride in the innovation and optimization of IP-PSTN call quality, allowing our users to make high quality phone and video calls at low rate….
Download the App HERE…
then register and invite your friends to use the app you will given instant #1000 via the app…..
Note that the app require Data to make calls
Download the app and start make free call to all network mtn,Glo,Airtel and Etisalat…..