Changing the ID number of your phone is as easy as swapping the font in a word processing document. Software programs that let you alter this 15-digit number can be readily bought via the web.
Some sites even sell “chipping” kits that bundle cables and software together into one package for less than £50.
With this software and a cable that connects the phone to a laptop or PC, the number can be changed in a few moments.
“It’s not very difficult; anyone could do it,” said Jack Wraith, head of the Mobile Industry Crime Action Forum.
He said different chipping programs changed different parts of the International Mobile Equipment Identity (IMEI) number borne by GSM handsets.
The 15-digit IMEI is programmed into a handset when it is manufactured.
It is made up of identifiers that reveal where the handset can be used, which factory made it, a unique serial number and a check digit that ensures the whole number is valid.
Like credit card numbers, only certain strings of 15 digits are valid. Chipping software is built using algorithms that work out valid combinations of numbers.
Mr Wraith said the software packages typically changed either the last two numbers in an IMEI or the entire 15-digit number.
You can check the IMEI number of a GSM phone, which prevail in Europe, the Middle East and the Far East, by dialling *#06#.
Mobile networks that do not use GSM technology do not use IMEI identifiers.
Mr Wraith said by the end of the summer all the UK’s mobile phone networks would be able to block phones by their IMEI numbers.
Currently O2 and Vodafone, which operate the UK’s oldest mobile networks, are the only ones that cannot block by IMEI number.
Laws being introduced in Britain will make it an offence to sell kits that allow IMEI numbers to be changed.
“There’s no legal reason, or very few legal reasons, for that number to be changed,” said Mr Wraith.
But he said the introduction of IMEI blocking might not reduce the number of phones being stolen.
“A mugger who takes your wallet isn’t going to leave you with a phone to call the police,” he said.
However, it would reduce the saleable value of a stolen phone to almost zero, he said.