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
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