If you're a T-Mobile customer and you need to know your PIN number, there are a few ways to go about it. The easiest way is to simply dial *#06# on your T-Mobile phone. This will automatically display your phone's IMEI number, which is also your T-Mobile PIN number.
If you're not able to do that for whatever reason, you can also find your T-Mobile PIN number by logging into your account on the T-Mobile website. Once you're logged in, click on the My Account tab and then select Profile. From there, you should be able to see your T-Mobile PIN number listed.
If you're still having trouble, you can always call T-Mobile customer service and they'll be able to help you out.