If you intend to buy the new iPhone 5 with 4G support. It is important to know that the Singapore LTE network is a dual band network supporting 1800MHz and 2600MHz. Unfortunately, the new iPhone 5 supports only the 1800MHz band, generally great for indoors.
As for Hong Kong, only SmarTone supports the 1800MHz band. The iPhone 5 will be compatible with SmarTone network. The rest of the operators do not support the 1800MHz band yet.
Here is a list of network the mode A1429 iPhone 5 will work on
Model A1429 (GSM model)
1 (2100 MHz)
3 (1800 MHz)
5 (850 MHz)
Germany
Deutsche Telekom
United Kingdom
Everything Everywhere
Orange
T-Mobile
Australia
Optus (including Virgin)
Telstra
Japan
Softbank
Korea
SK Telecom
KT
Hong Kong
SmarTone
Singapore
M1
SingTel
GSM model A1428*: UMTS/HSPA+/DC-HSDPA (850, 900, 1900, 2100 MHz); GSM/EDGE (850, 900, 1800, 1900 MHz); LTE (Bands 4 and 17)
CDMA model A1429*: CDMA EV-DO Rev. A and Rev. B (800, 1900, 2100 MHz); UMTS/HSPA+/DC-HSDPA (850, 900, 1900, 2100 MHz); GSM/EDGE (850, 900, 1800, 1900 MHz); LTE (Bands 1, 3, 5, 13, 25)
GSM model A1429*: UMTS/HSPA+/DC-HSDPA (850, 900, 1900, 2100 MHz); GSM/EDGE (850, 900, 1800, 1900 MHz); LTE (Bands 1, 3, 5)
802.11a/b/g/n Wi-Fi (802.11n 2.4GHz and 5GHz)
Bluetooth 4.0 wireless technology