I've done a comparison of 2 Bill Pay options (€45+€60) and the normal €20 Prepaid choice over 24months and used the Iphone X 64gb and 256gb handset costs.
With the Iphone X 64gb Bill PAY
With the Iphone X 64gb PREPAID
With the Iphone X 256gb Bill PAY
With the Iphone X 256gb PREPAID
I was under the assumption because you're contracted to 24 months there'll be compensation by being cheaper than buying it out right.