EDIT. vi3tboi781, when you click on the Setup Blackberry Internet Email link, that takes you to a https://bis.tmobile.com
You said you added the blackberry data plan to your account, right? Is your blackberry actually in the tmobile system? I don't remember exactly how to do it on the tmobile web site, but maybe you have to do that.
When you are on the my tmobile web page, at the top right where there is the link Support For My Phone, does it show your blackberry? If not, click the link Not Your Phone? and proceed from there.
Or call customer service.