I forgot to point out: the Android method for calls to come in while 1 is in use, is just conditional call forwarding. You can do that on the iPhone, that's what I do. But... they need to be from the same country. That's the reason why it fails, that I forgot to point out. The AT&T SIM has a US/Mexico/Canada plan. While I could place calls from any of those countries and to any of those, it would not let a call forward be activated. So, other people like me, with 2 sims from the same country, set a conditional call forward to the other sim, on each sim. Apple could do the same thing as Huawei and Samsung... and just do it for the users with the flick of a button. Anyhow... in your scenario, it can't work due to carriers not allowing the international call forward. Hope it's clearer.