5 Skype
Skype has been around for a while. And though it may not be as popular as it once was, long before carrier-based Wi-Fi calling became widespread, Skype was one of the most reliable choices for internet-based voices calls (VoIP, or voice over internet protocol).
The first Skype for iOS app was launched in early 2009, roughly half a year after the App Store first debuted. Like most apps of its time, it shared a rounded design aesthetic that looks fairly clunky by today’s standards. But it worked, and it allowed users to make free calls over Wi-Fi networks. Video calling was added later, around the time of the iPhone 4 in 2010.