I tried GreenAddress Ios app, the first mobile wallet for Ios that i know its using segwit, but i have a problem with the app, it don't remembers my wallet, i have to write the Mnemocis words every time that i want to log in.
I'm pretty sure that's by design. They probably don't want you to be storing your private keys on your phone. The main GreenAddress app is for PC. However, I believe they have a Green Bits mobile app that is a mobile wallet made by the same people.