CelcomDigi has announced that a scheduled Digi system upgrade will take place from 9pm on Oct 14 till 9am on Oct 15.
In a notice on its Help page, the company said voice calls, texts, Internet services will not be affected during the system upgrade period.
However, some channels and services will be temporarily unavailable including the MyDigi app, website, Digi online store, business portal and Digi kiosk.
It added that registrations (new registration, change of plans) and purchases of select value-added services, such as additional data, mobile app purchases and roaming passes, will also be impacted.
Billing and payment services such as prepaid reloads at conveniences stores will also not be available.
Customers should also be aware that one-time password (OTP) and transaction authorisation code (TAC) request will be temporarily unavailable during the period. The company advise customers to complete any necessary transactions in advance.
"Please remember to make your payments, reloads and complete any urgent service transactions before Oct 13 to ensure a smooth experience during the scheduled system upgrade," it said in the Help page.
It also issued a reminder to Fibre and 5G Home Wifi service customers: "To ensure continuous service during this time, please DO NOT restart or reset your router from 9pm on Oct 14 to 11.59pm Oct 16."
A full list of impacted services is available on the Help page.
Celcom services will remain available as usual during the scheduled system upgrade.