Buyer's Remorse Period (AKA Trial Period)
From HowardForums Wiki
This is a period of time in which you can terminate your T-Mobile service with no penalty. The length of time varies based on what state you live in; you have a 30 day time frame in California and a 14 day time frame in all other states. If you activated your service on T-mobile.com, then you have 20 days. This period starts from the day your service is activated and that is day 1. During this time, you can try the phone and service out to make sure that it will fit your needs. If not, you will need to return the device and everything that came with it, including the original packaging, to the original point of purchase and call in to Customer Care to cancel your service. The original point of purchase is where you got your phone, ie: the exact store, or if you activated online through T-Mobile.com, then your phone will need to be returned to the warehouse in Georgia. Other websites such as Amazon or Wirefly will have their own return policies, so please contact them if the situation calls for it. When you call in to terminate your service, the representative should remove any activations fees associated with the line(s) you are cancelling and then cancel the line for you. You will still receive a bill that will be prorated for the amount of time you had the service active, it does not matter if you didn't use the phone, the service was active.
If you port your number out, then the bill you receive will have your activation fee(s) on it, you can call Customer Care and they will be removed for you, the remaining balance will still need to be paid. Please be careful of this if you are porting, a port can take up to 24 hours to complete, if the line is cancelled on the day after the end of your remorse period, then you can be held liable for the ETF. A little planning can go along way towards preventing frustration to a rep that doesn't care to help you since you are not a customer.
Source(s): T-Mobile solutions