I would like to fly the Standard using a Iphone 5s since its compatible,and the phone I'm using now is not,just to see if I notice any difference. Is it safe if the Iphone doesn't have a sim card in it?
You will have everything but the map unless you download it while you are on wifi. I’ve flown a P4 and a Mavic Pro on a 5S without a problem. The iPad I usually use to fly does not have a SIM card in it. I am usually flying a Mavic Enterprise Dual.
I think there are cannot be any problems but I think that it is better to keep it on airplane mode, because we don't know what can happen. Usually I can use my phone as well and there are not any problems but I am always setting it on airplane mode so the pilots can see where they are going. You can see more information about broadband and mobile tips from experts. There is a lot of information about this things. Moreover they have different interesting life hacks that I am sure you will like.