My only question is, how much is the early termination fee?
It's based on how many months of your contract have been completed, and, as budone said, the type of phone you have.
Standard, multi-media and feature phones are $175 less $5 for each month completed. Based on your statement that your contract ends in December, your ETF would be $175-$100 (assuming 20 completed months) or $75 ETF.
Smartphones and Blackberries are $350 less $10 for each month completed, so $350 less $200 or $150 ETF.