I started using Zoiper on a tablet last December. I use several sipgate accounts and accept the default account settings and enter user / pass. Accounts register and I can make outgoing calls but I have never been able to receive a single call. I now have a new S6 and I really need to start using VoIP. Same problem with S6. I had all accounts working perfectly on old iPhone and they work with PC software. Just Zoiper not working!