Or quote on deliverables providing estimates for development time, then charge quoted prices for those deliverables (fractionally based on progress if the customer is hours-focused). Be honest about this.
So if you estimate something at 40h @$100/h and get it half done in four hours, bill 20h. This is a two edged sword — estimate well. (Do charge for scope creep though.)
I give clients the option of being billed this way or by the hour. The argument for this option is fixed costs and at least some guarantee of satisfaction. They're also paying for results and not activity.
