THE e-commerce bandwagon bypassed millions of carpenters, massage therapists, lawyers and other service providers, mostly because it is impossible to drop an appointment into a shopping cart without unleashing a scheduling nightmare.

“This is something that’s been needed for a while, but no one has been able to do it successfully,” said Greg Sterling, of Sterling Marketplace Intelligence, an online consultancy. “With these new services, there are a lot of circumstances where it can work quite well for both the business and the consumer.”

When Jennifer Brinn opened a practice in massage and Reiki (a Japanese stress-reduction technique) in San Francisco in 2003, she relied on a day planner and lots of “e-mail and phone tag” to book appointments. Last year, she began testing HourTown, an online booking service started by a former product designer for PayPal, Ryan Donahue.

HourTown, like its competitors, BookingAngel and Genbook, is an online calendar tool, with a twist. Users fill the calendar with personal and business appointments, but they can also transmit to the Web any blocks of time they would like to make available for business appointments. Customers can book a time directly from the service provider’s Web site, or, in the case of Ms. Brinn, they can reserve a slot and wait for her to confirm the appointment with an e-mail. Either way, it is free for customers.

Last year, Ms. Brinn started buying text advertising on Google around the same time she added the HourTown booking technology to her site (www.jbrinn.com), and since that time her client base has doubled to more than 200. HourTown, she said, helps her attract more impulse buyers.