Say I'm switching from at&t to t-mobile next month and am eligible for a full discount upgrade for the 5s. Are there any downsides to buying it from at&t for $200 + $36 activation fee + taxes, and then paying the $325 etf next month. The other option is to buy the t-mobile off contract version for the full $650 + taxes but I'm thinking I save $80 here. Are there any downsides that I missed to this (besides the hassle) if I'm definitely switching carriers? Are there any hardware differences between the t-mobile and at&t model? Any thoughts are appreciated.