for O2 (Hong Kong), software bundled in O2 Devices at Asia, embedded in ROM.
Dialling non-local number from mobile phone is extremely expensive when user is roaming overseas. Many travellers will prefer to use calling cards to make IDD calls when they travel aboard. Travellers can use their calling cards to make IDD by prefixing the calling number with the specific access code, calling card no. and passcode provided by the calling card company.