Is it a single line plan?
Is there a minimum commitment for the $60/m single line 2GB plan?
Why is there no clear cut answer on how to buy the phone with no contract subsidy. It's just crazy. I am not eligible for an upgrade, and want to pay full price, and they are making it tough to find out what I should do.
As long as the line that has unlimited is not actually using an upgrade, you will keep the unlimited. If you do an alternate upgrade and switch the phone over, you're fine.
Illustration:
Family Plan: Line 1 - 2 - 3
Line 1 has unlimited
Line 2 does not and has an upgrade.
Use an alternate upgrade on Line 1 based on the eligibility of Line 2. Basically, (the computer does all this) it's upgrading Line 2 to the iPhone 6, then switching it to Line 1, then moving the old phone back onto Line 2.