From internet-free voice-calling apps to Foursquare spin-offs, we covered a lot of ground with new iOS apps in May. So by way of a quick recap, here’s our pick of the best from the past month. Ringo While many apps have been challenging Skype’s throne in recent times, Ringo launched this month with a fresh take on what a mobile calling app can look like. Interestingly, Ringo doesn’t require an internet connection to make calls – it routes them in the same way a regular carrier does, so “calls are not affected by fluctuations in internet connectivity that often lead...

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