You can easily switch between T-Mobile, Verizon and AT&T. If you live in North America and have either iPhone 5S or iPhone 5c you are not locked to one of these carriers. Of course, you should understand how this works and why your device can support the SIM card of the company it is locked to and some other SIMs.
Step 1: Are You Eligible?
Step 2: Switch iPhone 5S / 5c to T-Mobile
According to T-Mobile, the devices sold in its stores are locked and can be unlocked after 40 days from the time you buy your iPhone.
Step 3: Switch iPhone 5c / 5S to AT&T or Verizon
According to Verizon, the 4G iPhones it is selling are always unlocked.
According to AT&T, the gadgets purchased from AT&T stores are locked but can be unlocked if you call at 800-331-0500.