50-50 on that. This code will bring up the IMEI (international Mobile Equipment Identifier) on GSM phones. I am not sure what it will do on Verizon or Sprint/Nextel phones.

The IMEI is a code that is unique to your phone (through the Snopes site you can see how the number is made up). I've got the complete algorithm around here somewhere.

In a normal call record (which comes over the switch to your cell phone company's billing system) this field is sent.

It is true that the cell phone carrier can put this on the EIR (Equipment Identity Register) and send it to the "CEIR" (Central EIR) in Ireland. Some do, some don't. But at least they can block it within their own network even if they dont send it to the CEIR.

Then the switch checks the EIR before completing the call.

This was a big problem we had in Zimbabwe. Lots of phones were stolen in South Africa and moved over the border for resale. When a cell phone was upwards of US$1000 it made sense. And since we (Zim) did not look at the IMEI, we didnt care that it was stolen. That changed of course, and we ended up blocking the phones on the EIR list sent by the ZA agencies.

Sorry - more than you ever wanted to know...