Can you switch ATT cell phones that are under the same plan because you want an iphone but you are not eligible for the cheap upgrade but one of your family members are and they dont want iphone?

Yes, I have done this several times. Basically the way it works is; if any of your phones are eligible for upgrade, they will sell you a new phone with 2-year plan at their current, new phone plan price; and since you can use any phone you own with any phone number on your plan, their rep will be happy to make that switch for you. BTW that is true of any phone ATT sells, not just iPhone, though I can't imagine why anybody would want anything else. Also, note when new phones come out they will often wave eligibility for new plan pricing if you are close to 2 years--they want to sell phones. I suggest you bring ALL phones under your plan to the ATT store with you and test a phone call on each one before leaving however, otherwise you will need to go back because ATT will likely mess up the switch--SIMS and all that can be very confusing.