I usually explain that development is an iterative process, and that I generally deliver work as soon as it's done.
We talk about the knobs that are available to tune the work to the goal, and how to measure goals. We talk about containing costs, and working together to deliver good value.
I find that in general, estimates are rarely, if ever, accurate to any significant degree, and thus are usually dishonest when presented as a way to assuage client anxiety over "when will it get done" or "how much will it cost".