I'm working on some content for PalmSource's smartphone initiatives (the Palm Powered Mobile World program), and I did an experiment tonight. Back in the Palm VII days, Web Clipping supported two special URL schemes, "palm" and "palmcall". I talk about these at length in my book, Palm OS Web Application Developer's Guide. Since the writing of that book in 2001, the browser landscape has changed dramatically. Web clipping is gone, and there are four browsers that share the market: PalmOne's WebPro 3.5 (based on technology from Novarra), PalmSource's Web Browser 2.0 (based on ACCESS Netfront), PalmOne's Blazer 3.0 (also based on Netfront), and Sony's simply-named NetFront 3.1 (guess who).
To test the browsers, I posted a simple webpage that had links to "palm:pref.appl" and "palm:pref.appl?test". In Web Clipping, this would launch the Preferences application using the sysAppLaunchCmdURLParams launch code, but with an empty string as the parameter. In my tests, both Blazer 3.0 and PalmSource Web Browser 2.0 did this correctly. PalmOne's WebPro 3.5 ignored the parameter string and just did a normal launch of the Prefs application.
I also went ahead and tested "palmcall" URLs using the UWBarChart example from my book. WebPro, Web Browser, and Blazer 3 all handled launching the bar chart plugin after I downloaded the UWBarGraph.prc file to the device, however the browsers had problems drawing some items on the screen after I dismissed the bar chart dialog box; I don't know if my plugin left the graphics system in a bad state, or if this is just a general problem with the ACCESS browser core.
The Sony Netfront browser had problems with everything. It didn't support either the "palm" or "palmcall" URL schemes, and it didn't even correctly handle downloading the .prc directly from my web server.
Now, there's no big reason to use "palm" or "palmcall" URLs if your application has good Exchange Manager support, but one area where a "palm" URL can be really useful is online help. If you've got an application that needs a hypertext manual, you can link to your website where you provide a help system using the device's own browser. To return to the application, you can have "palm" URL links that relaunch your program. If you use this method, you need to make sure that your application treats a sysAppLaunchCmdURLParams launch code like a normal launch; if you don't do this, it's likely that the link will just relaunch the browser, since your application will immediate exit.