• All CMHK customers can use Roaming Call Back Service directly without application or any deposit.
• In addition, you can also choose to apply CMHK's IDD Service, and make IDD calls to other countries/destinations when you are roaming abroad: Simply visit any conveniently located CMHK Shops or Customer Care Centre to register, and pay a refundable IDD deposit of HK$1,000, or register to settle your bill through direct debit from your credit card. One day to activate. All subscribers who have paid an IDD001 deposit can enjoy IDD Service while roaming without further registration.
• Activate or De-activate International Roaming Service:

  Activate International Roaming – Voice & Data (Able to use Voice & Data Roaming Service in worldwide)
  Activate International Roaming - Voice only (Able to use Voice Roaming Service only in worldwide, not include Data Roaming Service)
  De-activate All International Roaming – Voice & Data  (Once deactivated, the service cannot be activated overseas with above method)

  - Customer could make call to local number directly while roaming aboard. To make call to Hong Kong, you may press + 852 + (Telephone Number) or use Roaming Call Back Service. To make call to other country/destination, you may use Roaming Call Back Service or IDD001 Service. Customers are required to pay the related charges.

  - Customer must enable local data service (Press *106*01#) first before activate the roaming data service
  - Since part of the roaming operators do not support short code, suggest to activate or de-activate the International Roaming Service by pressing USSD code before leaving Hong Kong when necessary.

To effectively control data roaming usages and related charges, you may consider adopting the following measures according to your needs:

• If data roaming service is not needed when travelling abroad, we suggest you deactivate data service (Reserve Roaming Voice Service) by pressing on your handset before departing Hong Kong to avoid unnecessary charge, please click here for detail. Please note data charge may still be incurred even if you have turned off data roaming service on your handset.
• Double check that mobile data function remains switched off whenever you re-start your handset
• Check your data usage regularly -- by using your handset’s counter function, entering relevant short code () on your handset, or by logging onto CMHK website
• Check frequently that, while using Wi-Fi to access Internet, your handset has not switched connection using mobile data services
• Switch off the auto update / push email / push notification / location update functions of your handset or mobile apps if they are not needed
• Try to browse the “mobile version” instead of full version of websites (e.g. Facebook / Yahoo!) in order to minimise the data usages

Don’t do the following unless you really need to use the services, understand the nature of such usages, and know the expected data volume to be incurred:

• Open email attachments
• Visit websites which may incur high volume of data transfer (e.g. YouTube)
• Use mobile apps which may incur data usages
• Use instant messaging applications which may check your status automatically
• Use services which may incur high volume of data transmission, e.g. File transfer or music downloads
• Use applications which may incur unexpected or unknown volume of data transfer, e.g. Software or hardware updates / bit torrent / video streaming / mapping service (ie. Google Maps) / AGPS location update (i.e. use Geotagging in photo shooting)