Callers in areas including Bradford and Milton Keynes, will need to include the code for every phone call they make.
The changes have been put into place to free up new telephone numbers for areas where there is a high demand reported Mirror.
Usually, the code can be left out when calling local numbers from a landline,
At the moment it is impossible to create a landline number beginning in either of these digits because, without a code, the network would assume it was a mobile, or directory enquiries number.
This means that calls will fail to be connected, or connect to the incorrect number.
By introducing the changes, Ofcom hopes to make around 200,000 new numbers available in each of the five areas.
The change will be implemented across five areas of the UK
Aberdeen (01224): includes areas such as Aberdeen, Balgownie, Kinellar, Lochnagar and Portlethen
Bradford (01274): includes areas such as Bingley, Bradford, Horton Bank, Low Moor and Queensbury
Brighton (01273): includes areas such as Newhaven, Barcombe, Southwick, Brighton and Lewes
Middlesbrough (01642): includes areas such as Billingham, Easton Grange, Linthorpe, Middlesbrough and Stainton
Milton Keynes (01908): includes areas such as Bletchley, Milton Keynes, Newport Pagnell, Stoke Goldington and Wolverton