You can definitely build that contacts app as a web app on mobile safari. HTML5 appcache lets you take it offline, localstorage gives you 5 mb of storage, web sql or indexeddb gives you 50 mb. You can use something like pouchdb to give you a clean wrapper.

Yes, service workers would be nicer, but you don't have to go native to do an offline app on iOS. I built one years ago, appcache is good enough.