Only way either of those two carriers will do something like that is if one or the other does it! Those two carriers view each other as the only competitors, notice how each carriers plan and feature pricing is almost exactly the same!
As far as Sprint, they have been in financial flux for many years! Are they gonna go bankrupt not likeley but of all the carriers they are financially in the most unstable shape.
Well its no wonder they are not advertising it! No company likes to lose money. But damn they suck, I hated them when I had them. It explains alot when you talk about them not being able to count, becuase they sure wont or cant explain billing.