I was just doing patterns at OIIE when the controller switched. I was on Unicom for a period when no one was active, then someone re-took over when I was on base. They sent me an On Guard message but I was unable to find the frequency in the ATC tab or on the map, so I left the flight, fearing I was going to be ghosted.
I have an iPhone 6 if that makes a difference. IOS 11.4.1.