What part of "a contract stipulates the relationship between two parties" did you not understand?
It goes both ways!
That is exactly what contracts are meant to do, and have always been meant to do. And in order to use them successfully, they don't need to be "absurdly lengthy" or anything. The boilerplate you're referring to generally has nothing to do with "abuse" or "being reasonable", and most of it doesn't even need to be there, because if you'd leave it out, it'd be implied.
What you do have to do, however, is stick to the unique terms that you did write in your contract. And if you cannot, don't put them there, or don't offer the contract.
Simple as that. If you offer people unlimited phonecalls, you should be prepared for them to be on the phone 24/7. If you're not, you really shouldn't be offering them unlimited phonecalls, instead maybe offer them 20,000 minutes per month (that's about half of 24/7).
And if "twenty thousand minutes per month" doesn't sound as snazzy as "unlimited minutes", that's too bad because the reality of the matter is that you apparently cannot afford to actually offer "unlimited minutes".