The bandwidth caps and all included features were clearly spelled out in the entetprise contract and when we went over, they didn't push for a contract renegotiation unless the overage lasted like 3+ months. And we frequently got new features included in for free.
In fact, recently they asked to renegotiate the contract due to some obsolescence and we ended up significantly dropping the bill as a result. Kind of backfired on them, I wonder if the account manager is kicking herself for this.