UAProf production for a device is voluntary: for GSM devices, the UAProf is normally produced by the vendor of the device (e.g. Nokia, Samsung, LG) whereas for CDMA / BREW devices it's more common for the UAProf to be produced by the telecommunications company.
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This approach allows detection of devices modified by the user, Windows Mobile devices, Legacy devices, Spiders and Bots, and is evidenced in at least one commercially available system.