All complaints that I previously had about Ooma's iOS app have now been beautifully addressed with the July 31, 2017 update. OomaHomePhone has been optimized for iPad, all aspects of it function perfectly, and several new features have even been added. This is now a truly great app to use. Thank you Ooma.
(My former comments about issues now resolved: "I have only had experience with the Ooma app on iPad Pro 9.7 and iOS 10, so it may work better on an iPhone, or on an older version of iOS - but, OomaHomePhone is in need of an update. The volume control does not work, the mute control does not work, and OomaHomePhone 's display orientation is only correct when holding an iPad in portrait view. When holding iPad horizontally, in landscape view, Ooma's app remains oriented in the other position. There are a few other quirky things about OomaHomePhone I don't like as well, but if Ooma were to fix these problems, I would consider their app to be good. Until then, at least for iPad and iOS 10, I can only say OomaHomePhone is useable, but difficult.")