If you mess up the off-premise station mapping, yes.
Here's mine:
[tt]change off-pbx-telephone station-mapping 61569 Page 1 of 2
STATIONS WITH OFF-PBX TELEPHONE INTEGRATION
Station Application Dial CC Phone Number Trunk Config
Extension Prefix Selection Set
61569 EC500 1 - 6175551234 ars 1[/tt]
Now if I move the prefix 1 over to the phone number like this:
[tt] STATIONS WITH OFF-PBX TELEPHONE INTEGRATION
Station Application Dial CC Phone Number Trunk Config
Extension Prefix Selection Set
61569 EC500 - 16175551234 ars 1[/tt]
It will mess up the systems ability to map the incoming ANI to the extension of the user.
However, and this is big, it also messes up the system's ability to map the ANI of the cell to any of the feature extensions you might have setup. So if the user wants to activate or deactivate EC500 remotely, he can't just call a phone number. He'd have to dial into a telecommuting extension, enter his extension, an extension passcode, and then the EC500 activate or deactivate codes. None of the feature extensions will work for him at all.
The system will still extend calls to his cell when people call his desk phone, and he can still activate and de-activate the feature (though it's a little harder to do), but his cell will show up when he calls stations. Not his extension.
Carpe dialem! (Seize the line!)