Police are reminding residents that they will need to call the new non-emergency number when the old number is deactivated at the end of the month.
The number, 0345 123 33 33, was introduced on December 1 2008 as the new way for people to ring the force about any policing matter which is not a 999 emergency.
It was introduced following guidance given to all public sector organisations by the Office of Communications (Ofcom) to help eliminate public confusion over call costs.
It replaces the former number of 0845 123 33 33. The change was made so that call costs will be uniform whichever landline telephone company and call package people use. This is not true of 0845 prefixed numbers, where costs can vary.
The 0845 number will be deactivated on December 31 2010. People ringing this number will hear a recorded message asking them to dial the new number instead.
Deputy Chief Constable Alan Goodwin said: “We introduced a new non-emergency number because the old number could not be used as part of a free-call package and it was expensive to ring from mobile telephones.
“During the last two years, we have been gradually phasing the old number out, replacing it on documents, leaflets and other literature.
“We hope that by operating the two numbers alongside each other for the past two years, people will now be used to ringing the 0345 number.
On average, call operators at Derbyshire Constabulary answer 842,000 non-emergency calls each year.