Yes, each line has its own contract, and the terms are the same, even if it is a secondary line. Your ETF will be $175 if you bought a simple feature phone, or $350 if you bought an "advanced device" when you upgraded. The $175 ETF decreases $5/month and the $350 decreases $10/month for each month of the contract that is completed.
Remember what the ETF is all about. When you signed your contract, you got a new phone for a discounted price. You basically financed the balance of the price over a 24 month period.