I have exactly the same question. I haven't been able to figure it out. I stopped by a TMobile store today and they did not have the slightest idea about where to send the devices because when you buy it at the store, they take your old phone right there. I will call T-Mobile tomorrow in hopes of finding anything out.
I forgot to mention that I called T-mobile 611 for an answer and they directed me back to Costco. I called the Costco kiosk and spoke with the salesman who I bought the phone from. He said to use the website on the instruction form that he gave me and I have already tried that route! He said to come in and he would show it to me? That's why I'm here...I don't think he has the answer either.
The website is www.t-mobile/promotions. It was on the sheet that Costco gave me and where I started the trade-in process. The visit to Costco was of no help. The guy working there said his manager would call me...I'm not optimistic he'll have answer. It seems to me now that maybe Costco was supposed to take my V20(trade-in phone).
To add to this (because I have the exact same question), on the papers I was provided by Costco, on the 2nd page it says "How to Redeem Your Offer" with the following instructions:
1. <paraphrased, buy galaxy S9/S9+>
2. "Ensure you complete your trade in by sending your trade in device back through the T-Mobile/Assurant trade in process."
3. Go to http://www.t-mobile.com/promotions within 30 days from purchase.
4-6 is info on what you'll need to submit.
Is the idea to go through the standard trade-in process through the t-mobile website? And somehow (through internet wizardry or a functioning account system) t-mobile will be able to link the trade-in with the already-started promotion process?
Hey folks! The trade-in will be done through our standard trade in process. If you did not receive a shipping label with your new S9, please go to my.t-mobile.com and follow these steps.
From My T-Mobile, select Phone.
Select Trade-in status.
Select the offer for the applicable trade-in device.
Select the “+” to review the offer details under Trade-in Device. You will have access to print the label from this site.
After sending in your trade-in device and within 30 days of purchase, go to www.T-Mobile.com/promotions.
T-Mobile Phone Number
T-Mobile Account PIN
Promo Code: C18SAMTRADE
IMEI of device (Dial *#06# from your device to obtain)
Upload a copy of your receipt and an image of your device box IMEI as proof of purchase.
Well, they don't have the slightest idea about this at my Costco. I was able to process the 175 dlls promotion, I'm supposed to receive the rebate in a few weeks, but still no idea on how to send the device, which is just worth 25dlls (trade in value). If I find anything out, I'll post it here.