Yes, you can trade bonds through iOCBC provided they are listed with SGX. I believe you can buy/sell through POEMS as well. Try look for JTC bonds!
These bonds are normally not liquid, so be careful! You only buy and hold them using your excess money.
Most of the bonds issued by Singapore government are not listed with SGX and they are only sold to big institutions and funds. Those that you can see from SGX are bonds that issued by Singapore government linked companies or/and authorities such as JTC, HDB etc. and some big companies eg. SKM etc.
