Ruling on exchanging an old phone for a new phone, and paying a sum of money in return for that
Question

                what is the ruling of exchanging items with a company?
my example:

my sister has an iPhone 4 and she has had it for 1 year, she bought it from someone else who had it for about a year and a half. her iPhone 4s screen is cracked. she wanted to go to the apple store and give them her iPhone 4 so they can fix the iPhone. the way they deal with it is if you don't have a warranty you pay them $100 and they give you a new iPhone 4, i told my sister that you can pay them and extra $100 or $200 and you can get an iPhone 4s or an iPhone 5. Technically you have already paid for an iPhone 4 and you are adding the left amount of price for the iPhone 5 or 4s. my mum said ibdaal is haraam and that this is ibdaal, is this haraam?
Praise be to Allah.
    This 
    transaction that your sister wants to do, to exchange the damaged phone for 
    an undamaged phone, and paying the difference to the company is a 
    transaction that is permissible according to Islam. There is nothing wrong 
    with it, because mobile phones do not come under the heading of the 
    commodities in which it is stipulated that any exchange must be 
    like-for-like in order to avoid riba. Therefore there is nothing wrong with 
    exchanging a phone for a similar phone or one that is better than it, 
    regardless of whether or not she pays an extra amount of money. In fact she 
    is buying the new phone from them and paying for it by giving them the old 
    phone plus this additional amount. 

    We 
    have previously discussed the types of commodities in which it is haraam to 
    give more in return for less (of the same commodity) in order to avoid riba, 
    in fatwa no. 118149 

    And 
    Allah knows best.