I prefer coming to Costco to do my upgrades via Wireless Advocates for my tmobile account. The staff is great and is always willing to help out. Gustavo usually helps me with all of my upgrades and I have nothing but good things to say about him. You dont get charged assistance fees and SIM cards fees like you would in a Regular tmobile store. I even qualified for 2 $30 Costco cash cards by doing 2 iPhone upgrades here. Thank you !