Although I clicked on jpo's link to sign up, I did not see any credit applied to my account, so I contacted ting. They said it didn't look like I had used a referral code, but they were happy to apply it at that time. I immediately saw a credit under my "billing history" tab in my ting account. The customer service rep also claimed that jpo should be able to see his credit now as well, even though I just signed up, brought my own device and haven't paid my first bill yet.
If you don't see a credit when you sign up, investigate with ting. I found them very helpful.