During the transitional period, users can make calls using both the old and new codes.
This phase will change the codes for Hanoi, Ho Chi Minh City and 21 provinces in the southern part of Vietnam, where there are 3.07 million or 58% of Vietnam’s total landline subscribers.
The new dialling codes for Hanoi and Ho Chi Minh City are 24 and 28 respectively, while those for the other provinces and centrally-governed cities are in the form of 2xx.
The first and second phases of the code switching scheme were completed without any disruption to telephone communications.
The new area plan was announced by the Ministry of Information and Communications in November last year, in a move deemed necessary to clean up the disorder in telephone numbering.
For years the division and merging of administrative units have made the length of area codes between provinces inconsistent, with some province having codes consisting of three digits and some consisting of only one or two digits.
The same occurrence is also seen in mobile numbers which have prefixes of different lengths.
According to the Vietnam Telecommunications Authority, the number of mobile subscribers in Vietnam currently accounts for 95% of all phone users, while landline numbers now make up just 5%.