Hi Cletus,
I've looked everywhere Mobile PC stores files and there is nothing there that could contain an alternate tone. It looks like it's either built in to Mobile PC or else Mobile PC is using one of Windows alert tones.
If it's built into Mobile PC you're out of luck. If it's using one of Windows alert tones you can mess with the Audio Properties/Sounds.
If you have a speaker (Volume Control) icon in the System Tray, right-click it and select Adjust Audio Properties, then click on the Sounds tab.
If you don't have a speaker icon in the system tray, go to the Control Panel and select "Sounds and Audio Devices" and click on the Sounds tab.
That's a real long shot and it's not going to be easy to figure out which "event" (sound) is being used by Mobile PC. The quickest way to check if this will produce anything useful will be to click the dropdown selector for "Sound Scheme" and select "No Sounds". Then run Mobile PC and see it the alert beep is still there.
If it is still there, it's built into Mobile PC.
If it's gone, then you can play with the different events to see which one it is and change it.
I'll leave it to you how badly you want to chase this.
...ken...