Kennst Du Voice over Wifi?
Falls nicht, das bieten mittlerweile die meisten Mobilanbieter an, um schlechten Empfang auszugleichen, vielleicht mal testen.
https://www.google.com/search?source=hp&ei=jNj8XImSJcvlmwWduLHICg&q=iphone+voice+over+wifi&oq=Iphone+voice+over+wif&gs_l=mobile-gws-wiz-hp.1.0.0j0i22i30l7.3013.27299..28620...0.0..0.325.2490.15j3j2j1......0....1.......8..41j46i131j0i131j0i10j0i22i10i30.SviuP2LuwWw
https://www.google.com/search?source=hp&ei=jNj8XImSJcvlmwWduLHICg&q=iphone+voice+over+wifi&oq=Iphone+voice+over+wif&gs_l=mobile-gws-wiz-hp.1.0.0j0i22i30l7.3013.27299..28620...0.0..0.325.2490.15j3j2j1......0....1.......8..41j46i131j0i131j0i10j0i22i10i30.SviuP2LuwWw