Simply just a movie mistake.. I thought they would have fixed it but since the movie was out 2 days ago (15/06/2017) they cannot fix it. Just sloppy filming in my opinion.
(above is the actual movie mistake)
It could however be sponsored by iPhone but I highly doubt it because according to Forbes the movie is projected to make 53m (USD) and has already made 13m in 2 days!
I cannot think of anymore explanations other than that but I have found a YouTube video that supports your claim :
50 cent posted this on his Instagram:
When you look at this 2 PAC movie, and I know you want to say I'm
hating. But there's a scene in it where faith and PAC are taking a
picture and THEY HAVE A FUCKING IPHONE IN IT. what the fuck is this
He deleted the actual post but here is my source:
I could not find any footage of the scene where she does it but I am going to take 50 cents word for it and just say its a blooper.
He put another post up stating his opinion on the movie: