The $25 off the $40 subsidized line fee is a 62.5% discount, for those playing the numbers game at home.
A few more numbers of note:
The unsubsidized line discount of $25 totals $600 over 2 years, while the difference between the subsidized iPhone and the unsubsidized iPhone is only $450, so if you subsidize without a corporate discount, you're paying an extra $250 for your phone.
A 22% discount makes the line fee $35.20 per month. The unsubsidized line fee at 22% off is $13.20. The difference ($22) over two years comes to $528, which means even if you have a corporate discount, if you're subsidized you're still paying $178 more than you should for your phone.
This doesn't sound right. Everything I see is more than my legacy plan. If I get off contract, they aren't going to discount me $25 per line. So I am not sure where you are getting your numbers. Maybe you need to show us your phone bill..