In my case, I gladly give estimates over the phone. 99% of my business is residential and I price by the square foot, so most estimates are easy. (1 or 2 story - it doesn't matter. In fact, 1 story homes can take longer to do, since they have [sq ft being equal] more soffits and have a larger footprint, which means pulling more hose.) I advise the caller that there are variables that can affect the price, but since my price includes almost everything, it boils down to the P.I.T.A. factor.
While I may have had a few competitors checking out my pricing, most are not. I know because most schedule either an appointment or a visit to give an in-person estimate - which I offer. Most people are just glad to have a real person to talk to and not have to play "telephone tag" that they schedule on the first call.
I'm not saying this will work for everyone, but it absolutely works for me. At 10 mpg, not to mention the time, the less driving - the better.