T-Mobile Website now through
The SIM kits consist of a SIM and an activation code. The activation code is required when activating a new line of service on any T-Mobile prepaid plan including the $30/month 5 GB of data, unlimited messaging and 100 minutes plan, which is only available with new online activations.
By themselves, without the activation code, these SIMs can also be used as replacement SIMs for prepaid or postpaid accounts or to activate a supported tablet on any T-Mobile mobile broadband plan including the 200 MB/month free plan.
Update 4/30: the sale has been extended through May 1.
Related post: Prepaid Operator Profile: T-Mobile