TrueSwitch is especially popular with people leaving AOL. That's partly because AOL is the largest dial-up ISP, and it has been bleeding members to broadband services offered by cable and phone companies. But it's also because, unlike many smaller ISPs, AOL has deliberately made it hard to switch by using proprietary software and formats from which it's difficult to extract data like e-mail and addresses.

To be fair, AOL recently began loosening this tight grip on your data. It now offers a free utility that can synchronize your address book and calendar with either a PDA or with Windows programs like Outlook, Outlook Express and the Palm Desktop. You can download this tool at AOL keyword: "Sync." But this approach doesn't handle e-mail or Web favorites, and it doesn't notify your contacts you have a new e-mail address.

TrueSwitch has four functions. First, and most importantly, it copies your data from your old account to the new one. This includes stored e-mail messages, address-book entries, and, where relevant, calendar entries and Web favorites, or bookmarks. If you are using software like Outlook or Outlook Express to manage the new account, most of these items are transferred there. Favorites wind up in Internet Explorer.

If the data are stored on the ISP's servers, as opposed to your own PC, it can take up to 24 hours to accomplish. The e-mail, addresses and other data aren't deleted from your old software, merely copied.

Secondly, TrueSwitch will send an e-mail to everyone in your address book, notifying them of your change of e-mail address. You can personalize this message. Third, it will forward e-mail from your old account to your new one for up to 30 days. Finally, it will provide instructions on how to cancel your old ISP account.

The software itself downloads quickly and takes the form of a simple, step-by-step "wizard." It even detects all your accounts automatically to make it easy to choose the old and new accounts for switching.

TrueSwitch can be run in two modes. You can use the "Express Switching" mode to have the software perform all the functions in a standard manner. But I recommend the "Custom Switching" mode, which allows you to pick and choose among parts of the process. For instance, you could fetch your data but decide not to send the change-of-address notices or to forward e-mail. You can also specify which kinds of data to import, which people to notify and so forth.

In my tests, I successfully transferred my e-mails, address book and favorites from AOL to a Comcast cable modem account I manage via Outlook Express. I also successfully moved my data from a Web-based Hotmail account to an Outlook Express-based e-mail account provided by a small regional ISP. In both cases, everything worked fine, although I didn't have any calendar entries to test and I didn't send change-of-address notices.

I did run into a few annoyances. When you download the software, it automatically installs itself and starts running, whether you're ready for it or not. Also, TrueSwitch doesn't transfer old e-mail from AOL, only mail in the in box.

Finally, TrueSwitch installs one of those irritating modules that run constantly in the tray at the lower right corner of the Windows screen. This is ostensibly to be able to send you messages about the progress of your account switch. But I think it's at least partly to try to tempt you to buy other Esaya products, like a pop-up blocker and a spyware detector. There's even a "system checkup" function that purportedly finds problems and then recommends the company's other products as solutions.

All in all, though, TrueSwitch is a good product that solves a real problem.

Write to Walter S. Mossberg at mossberg@wsj.com¹