Most everything cell depends on IMEI
I travel both regionally and internationally frequently and Border Plod/ICE people having taken on an obscene interest in cell handset usage.
At first I simply travelled without a SIM, which defeats many of the simpler customs inspections techniques. Later, I was advised, they don't need a SIM as they can use the IMEI (serial number) with an on-line connected computer.
The GSM Association is the issuing authority for IMEI numbers and now governments access it's database for IMEI information.
Since I acquired a smartphone I have used an App that can change/re-install IMEI numbers, which I do weekly. Or before international travel. NOTE that it is essential you use a cell handset with a modified IMEI in the COUNTRY THAT ISSUED THE SIM as ROAMING CALLS are checked against that Cellco's database. I never use a SIM in my smartphone - only buffered WiFi.
Now that Border Plod/ICE men are getting smarter an 'inappropriate' IMEI number (using a Samsung IMEI number on a Motorola handset) will be kicked out, raising their hackles a notch or two.
On my Android device I refuse to use 'included' software opting for Third Party software that is less, or even non-responsive, to these intrusions. This means by keeping all my data on an SD card, removed and secreted on my person during travel, there is precious little to interest them. My ever trusty 'diversionary' but ancient Mitsubishi Trium handset, lacking even GSM ability, is usually sufficient to distract the inquisitors. A film or two also helps quell interest.