I've been with AT&T for a while but just last year I purchased an iPhone 4. Now that the update has came along I've realized I do not have enough space on my phone for that and deleting things would I would loose more than 80% of all the things on my phone (I have 8GB). So I was wondering, if I take my phone to AT&T would they charge me full price of I go and get an iPhone 4 with 16 or 32GB? Or would they just take my phone in the condition it's in than subtract the cost (it works fine expect the lock button does not always work).