Device limits on the Next program

Let me just state how incredibly frustrated I am that consumer accounts are limited to only four lines on the next program.  Because at&t chooses to enforce a device limit as opposed to a credit limit (which is what ALL the other wireless providers offer with their installment programs) it will be impossible for me to put any other line on my account on to your next program... regardless of how much we pay off the other lines, unless they are paid in full... at which point that line would want to upgrade again any how.  

The only option I have for my other lines is a 2yr contract.... but as soon as I put that line into a new 2yr agreement, my access fee will shoot up from $15/month to $40/month for the next 24 months of the contract.  Let's do the math...

$25 x 24 = $600, Subsidized phone cost = $199, Upgrade fee cost = $40

A grand total of $839 for a 2yr contract upgrade as opposed to...

Financed device cost = $27.09 x 24 = $650.16

That is a blatant rip off and a HUGE slap in the face to your loyal customers already on larger family plans.  I understand the need for limits when it comes to financing these various devices, but I think it's to have a device limit as opposed to a credit limit... by offering a credit limit you could greatly improve the flexibility to larger family plans and allow them to plan upgrades based around their given credit line at the moment.  It also should be more clearly represented by your sales reps.  This problem happened when one line broke her phone over the summer and went into a store to get a new phone.  She still had about a year left on her contract but was next early upgrade eligible.  She got a new phone by putting it on the next program.  Meanwhile another line on our account was planing on upgrading to the new iPhone 6 in the fall. This line was already out of contract as he was patiently waiting for the new iPhone to be in stock... when we were finally ready to upgrade this line, we were then told that the only option was a 2yr contract.  Talk about a huge disappointment for that line.  Here they waited patiently, were out of contract and had it all planned out... because of the fourth lines upgrade and the lack of clarity given to that early next upgrade done about a month earlier, the fifth line now had to pay almost $200 more to have the privilege to upgrade his line.  Because he has to pay for his monthly portion of the monthly bill and now has the addtional up front phone cost and upgrade fee to consider, he has chose to not get a new phone.  

at&t needs to come up with a better way to apply limits to the next program instead of some vague device limit which is a completely vague way to establish credit limits.  This is one area were all three of the other big players have you beat!