Absolutely, there are standard ways to handle this in a contract. Examples include Terms of Service, Service Level Agreement, and Scope Of Work.

Here's a simple example, from a company I don't have any connection with.
Best Value DNS Pricing | DNS Made Easy
"Hi, I'm a customer in your entry-level bottom tier and you haven't called me back in ten minutes so I'm gonna sue you..." see how this up front expectation is clearly defined?

 

Yes, that's exactly right. You might get in trouble with the word "unlimited" in ads, if there actually is a limit*

*unless you have a footnote like this in the ads. Might be worth while to check with a local attorney to be on the safe side.

Otherwise, maybe there's another term that would help? Extensive, always there for you, comprehensive service, done-for-you service, complete turnkey solution, etc.?

 

One last thought that came to mind. You might want to make sure to go over the terms one last time as part of your sales/ordering process. "I just want to make sure that we have the right option for you here, you're choosing the 50 updates per month, 100 hours per month plan at $x per month, with the 5% discount for prepayment, is that right?"

 

Well, I was thinking of this at the very end of the sales conversation. I personally am not a fan of surprise upsells, although I know some businesses succeed with them.

Earlier in the conversation or checkout process, you would have the chart that shows the different plans, and the available upgrades. Basic-Extended-Deluxe for the columns (or Bronze-Silver-Gold, whatever names you want to give your standard packages). Number of updates, amount of service time available, monthly price, minimum number of months, response time etc. for the rows. Then, for $x you can add an additional 10 updates per month, which roll over to the next month if you don't use them, and for $y you can get an additional 20 minutes per month, which don't roll over if you don't use all your available time each month. (Or whatever specific numbers apply to your offer.)

You then go over the option the customer chose one last time, just before you take their money, to be sure that you and they both understand exactly what order they want to place with you.