People living in Bournemouth, Poole and Christchurch will have to dial the 01202 area code when making a local call from the November 1st.
From 1 November, callers who omit the 01202 code when dialling locally will hear a free message telling them to include it when they redial.
This change is designed to safeguard the future supply of landline numbers in the Bournemouth area and avoid the need to change existing phone numbers.
Ofcom is working with communications providers, the local council, local consumer and business groups and charities to inform the community well in advance of the need to dial the code.
For further reading, please visit the Ofcom webpage.