Initially deployed in Newcastle, NSW, Singapore Telecommunications (Optus) have released their 4G LTE network in response to consumer demand for faster speeds, reduced latency, and perhaps most importantly to take the pressure off existing 3G internet services. Optus have since expanded the 4G network to Melbourne, Sydney, Brisbane, and many of other major cities. The continual rollout process will see Optus 4G arrive soon at most major regional cities and towns during 2013.
The Optus FDD-LTE service has been currently rolled out on the 1800MHz network with 10MHz of bandwidth. Their operating frequencies are as follows:
Transmission Downlink: 1840MHz - 1850MHz
Transmission Uplink: 1745MHz - 1755MHz
Up on the tower Optus are using Huawei network infrastructure, and Argus CNPX308 sector antennas. This type of antenna broadcasts the Optus 1800MHz 4G service in MIMO ±45° slant polarisation with an EIRP of around 35Watts. The emission designator for Optus 4G is 10M0W7D-- (from ACMA records).
Recently Optus has acquired 98MHz of continuous spectrum on the 2300MHz band from Vivid Wireless. Vivid Wireless currently have a WiMAX service deployed on 2300MHz offering customers speeds between 1Mbps and 12Mbps with most customers experiencing around 4Mbps download @ -75dBm RSSI (with a theoretical maximum of 36Mbps down and 4Mbps up). These comparatively poor speeds are the result of the higher broadcast frequency resulting in extremely limited range and signal penetration, as well as the underlying WiMAX technology.
Optus have plans to convert the 2300MHz band into a TDD-LTE service. TDD differs from normal FDD-LTE services by using only one frequency band to serve as both an upload and download channel. This means that 98MHz of spectrum must be shared between both upload and download, and while this may offer some benefits in dynamically scaling back upload bandwidth to support higher downloads (or vice versa), this means that we shouldn't be quite as excited about the 98MHz of bandwidth as we might have initially been.
Currently the Optus 4G network on 10MHz of bandwidth should be technically able to offer a theoretical maximum speed of about 69.7Mbps but real world expectations would be equal to Telstra's 2Mbps-40Mbps typical speeds. Note that Telstra 4G in QLD/WA/SA/NT can reach up to 88Mbps on 15MHz of bandwidth (with a theoretical max of 104.8Mbps). Hence we can expect Optus 4G to be significantly slower than Telstra 4G when deployed outside of the south-eastern states.
An Optus press statement  states that the dual band 4G network will be capable of offering "typical download speeds ranging from 25Mbps to 87Mbps". These figures have been adapted from TDD-LTE tests conducted by Vivid Wireless in 2011  which resulted in a peak speed of 127Mbps (average of 94Mbps) under controlled conditions.
. J. Drayton. Author. (2012, June 19) Optus to deliver a faster 4G future [online]. Available: http://www.optus.com.au/aboutoptus/About+Optus/Media+Centre/Media+Releas...
. D. Ramli. Author. (2011, February 7) Vividwireless adopts Huawei TD-LTE for east coast capitals [online]. Available: http://www.arnnet.com.au/article/375699/vividwireless_adopts_huawei_td-l...
TDD White Paper: http://www.tdia.cn/test/en/downloa/20111214.pdf