Oh, I see. What you propose appears consistent with what works with the grandfathered plan.
I'm have that discount also.
I am a bit nervous about my $20 not coming off the 2gb plan i just switch one line to. However I did ask for a supervisor when the first rep had no clue. She stated she checked after the change to 2GB and said she did in fact see it under my promotions section still. I got her ID and name etc, she said she noted my account and if for some reason it falls of she would setup a reoccurring credit. So we shall see. The spare line was just that a spare unlimited data line because it was so cheap but I don't really use it in anything so I figured being able to cycle three upgrades (worth $450 a piece in subsidy on iphones) was worth having a 2gb plan instead of unlimited on that line, so long as my bill doesnt go (if I lost the $20 off)