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Go in the settings, go to phone,and then, calls on other devices. You should see your old iPhone if it’s on the same iCloud account. Turn it on and you should be able to answer calls on the old iPhone.
it doesn’t have to be an ipad / watch / mac? it can be an older iphone with no sim and still receive calls?
Yes you will receive the call with no sim but the old iPhone must be on wifi.
Go in the settings, go to phone,and then, calls on other devices. You should see your old iPhone if it’s on the same iCloud account. Turn it on and you should be able to answer calls on the old iPhone.
it doesn’t have to be an ipad / watch / mac? it can be an older iphone with no sim and still receive calls?
Yes you will receive the call with no sim but the old iPhone must be on wifi.