I think you're overreacting. It's just a phone. I don't see the harm in letting her chat with her friends.
I see your point but I would not consider all of these girls as "her friends", one she didn't know at all and I only know one of the 4.
Also it would have been kept a secret which I don't like.
I didn't make a huge deal about it because I want her to tell me things.
I just told her in the future I want to know who she was talking to.