I’m glad to have seen this thread, only because I don’t have to disagree with many others, including ROB, on this one.
Lifi Aniyas Da’ati, and those are the key words, I can’t understand how one is passul as an Eid just because he uses an iPhone.
I tend to agree with the gist of what ROB said, which is that if a talmid chacham who sinned by day still merits “al tiharher acharav baLayla”, then even if a person did do some aveira with that phone (though there is no reason to assume he did so just because the device is capable of all sorts of things) then maybe he already did teshuva and is therefore just as kasher to be an eid as anyone else.
Perhaps someone who knows can enlighten everyone.