Three Hong Kong mobile service operator -- CSL, SmarTone, and 3 Hong Kong -- announced Monday that they will continue to offer unlimited local data service plans to customers in Hong Kong, but will apply network priority management in real time to ensure fair network access.

Another mobile carrier PCCW Mobile however has ceased all unlimited mobile data service plans on Monday.

Last November, Hong Kong's Office of Telecommunications Authority issued the mandatory fair usage policy setting out the relevant guiding principles for compliance by mobile and fixed broadband service providers. Service providers apply an FUP to ensure that their customers have a fair opportunity to enjoy and access their services and to prevent possible abuses by a small number of users.

According to the three operators, under their new policies, customers on unlimited plans who reach 5GB of local data fair usage within a single billing period will be given lower priority to access the network for the remainder of that billing period.

Customers continue to have unlimited access to the network without any additional charges, without speed throttling, or switching off of their service, the operators said.

"As we announced in early 2011, CSL's intention is to complete the move to volume-based pricing before the end of 2012," said Mark Liversidge, chief marketing officer at CSL. "However, we believe our customers need more time to understand their data usage behavior before moving to volume based plans. Therefore, we will continue to offer unlimited data plans and provide tools for customers to clearly understand how much data they use."

The operators said that the broadband experience may be affected when the traffic generated by broadband customers on a specific cell is extremely high, adding that users should see no impact to common Internet usage but may feel some impact on data rich applications such as high volume peer-to-peer services.

Amy Lung, chief operating officer (Mobile) of Hutchison Telecommunications Hong Kong said that the vast majority of customers will not be affected since 97% of the firm's mobile data users consume on average 5GB or less every month.

CSL noted that the firm will notify users -- along with available customer service apps on iOS and Android -- before their priority is being lowered, adding that it will also provide an online data calculator on its websites for customers to gauge their expected data usage requirements.