Yes, all the time, because people like to know over the fone.
Fact is, you can charge what you like per hour, if the cleaning is no good then its a futile exercise. A per-job price means an agreed list of jobs is done for an agreed amount of money, and then everyone wins (usually).
If your other local cleaners are only willing to quote and not give an hourly rate, then you're ok, because you're all pulling in the same direction. Only if they are charging hourly rates (which i doubt) should you consider changing your structure.