I currently have Galaxy Ace which has about -$100 on it's Tab. I would like to upgrade to a Nexus 4 on Tab Medium. How does this work? Do I pay off the remaining 100 dollars and get a new phone, or does the $100 count towards the new phones tab?
A Tab Medium allows for a maximum balance of $300 towards a subsidy on a phone. Since you already have -$100 on your Tab, upgrading to a Tab Medium would allow you to get a $200 subsidy on the phone of your choice. Since a Nexus4 is $300, you would need to pay $100 upfront for it as you only qualify for a $200 subsidy.