Dr. Phonez (same shopping center as Guitar Center, across from Northstar Mall) had really good reviews when I used them. My phone had a cracked screen, but functioned flawlessly. After one hour in their shop, my touchscreen only worked if I bent the iPhone down the middle. I gave them two or three tries and ended up having to upgrade my phone to get out of the situation. The ladies who work at the counter are also in desperate need of some customer service training.
This review doesn't really help you find a place, but I feel it's my civic duty to destroy this awful establishment by any means necessary.