Deals for current customers

I've called customer service twice trying to get a deal as a current customer. The first person started to make a deal, but then I had to leave and couldn't finish it. The second time I called I was told there was no deals available without trading in my phone or porting in a new number. I'm trying to upgrade my phone, without trading it in, so I can add it as another line on my account. Why are deals only allowed for new customers? Seems like a crappy way to treat loyal customers.