Viet Nam is ringing in changes next month to make way for a standardized phone numbering plan, but is struggling to get through to businesses hung up on how much it will cost them.

The government abruptly announced changes to millions of phone numbers from March 1, keeping its business community on edge about forking out money to replace everything from shop front signage, banners on trucks and buses, and neon-lit taxi signs to business cards, letterheads, invoices and brochures.

A woman (C) types on a mobile phone along a street in Ha Noi February 2, 2015.  (Photo: Reuters)

Cellphone usage is rising fast among Viet Nam's 90 million population, two thirds of which is under 30.

Active mobile numbers grew 12 percent last year to 138 million, reflecting a trend among the Vietnamese of having more than one handset in an expanding economy with a tech-savvy middle class.

In a country with five mobile phone operators, the change in phone numbers is part of a complex market restructuring process. Authorities say this will standardise existing numbers to make room for future growth, and they have no choice but to act now.

"Over these 50 years, the environment of telecoms business and telecoms technology has changed swiftly," Le Nam Thang, Deputy Minister of Information and Communications, said in a January directive announcing the changes.

All 11-digit mobile numbers are be shortened to 10 digits, with new area codes assigned to 59 of Viet Nam's 63 provinces. The old numbers would work for a while during the transition period, but companies are gearing up for a cumbersome exercise.

A separate government project to give each citizen a new identification number by 2020 is already causing bureaucratic headaches. Bank customers complain they're turned away by confused clerks or made to undergo verification procedures because their new ID numbers don't match records.