Haha, this is the same problem I encountered except my mom is the primary account holder.
You pretty much just have to read the phone number that was printed on the letter to the sales rep. The phone number isn't the 866 number or whatever, its more than likely the primary account holder's number (so your number). I'm using my mom's upgrade in order to get the $100 off the $200, so in short you'll get your storm for $100. Not a bad deal at all.
Just look for the thread that has the scan of the flyer sent out in order to get the number to call. Sorry I don't have that number handy... Actually I forgot I saved it into my phone. The number to call is 1-888-324-3310. You'll be asked if your calling about a flyer or coupon you got (something like that). Just say yes and then you'll be put straight through to a rep. Good luck.
