I have recently been doing quite a bit of windows mobile development -- primarily GPS and Radio Interface layer (RIL) coding. This is to further my research on resource availability related to cloud computing. I'll post a paper shortly. Anyway I was have trouble getting the VS cellular emulator to work. Found a link to help. Credit goes to Scott Savage. His blog can be found here:
http://www.scottsavage.net/2009/02/com-17-is-used-please-verify-in-cellular-emulator/

As usual I post a copy for archival purposes.

When starting the Cellular Emulator included in the Windows Mobile 6 SDK I received an error “Com17 is used please verify”. This is a particularly annoying error because it completely prevents the program from even starting. Where is the setting to manually select a COM port?

Anyway I managed to stumble upon a solution on the MSDN FORUM and I am reposting it here so other people find it a bit more easily:

Disabling modem devices in Device Manager

1. Open Device Manager and disable any Bluetooth, Modem or other devices that use a COM port (see picture to the right)
2. Open a new command prompt and execute the following commands:

   “C:\Program Files\Windows Mobile 6 SDK\Tools\Cellular Emulator\InstallXPVCom.exe” UnInstall
   “C:\Program Files\Windows Mobile 6 SDK\Tools\Cellular Emulator\InstallXPVCom.exe” Install

3. Start the Cellular Emulator
4. Re-enable any devices you disabled

The best part about this fix is that it is permanent. No need to disable the devices every time you start the Cellular Emulator, it remembers how to make everything work properly. Why couldn’t it do that in the first place?

UPDATE: A FAR SIMPLER SOLUTION:
If someone is still in trouble with this, I've just solved my problem by simply doing this :

- Open Regedit
- Go to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\xpvcom\history\group
- Double-Click on the entry named '6', the one with a value equal to 'COM17< -->COM27'
- Clear the value so that you still have the entry named 6 but data is empty
- Start Cellular Emulator