Yea that link is broke right now, Been reported and being looked into.
Here is another way posted by astrobill;
I found another way for us to view the contract details for each device on our accounts while we wait for them to fix this.
First, click on "See all usage" for one device.
Now, look to the right for a small frame containing the "I want to..." options again...click on "See my contract details" and it now DOES bring up the contract fulfillment date properly.
On the "My Account" page, Scroll down to the phone you want the information for, Hover over the blue "I Want To" and in the pop up will be "See My Contract Details" When you click on it you will get a pop up with the contract end date.
I'd like to know when my contract ends by checking on their site but cant seem to find the date. Is there somewhere on the site that states the date i have overlooked or do i have to call customer service.