To help the consumer have a better understanding on DiGi broadband and 3G, DiGi people will tell you that broadband is for your desktop access to the Internet, 3G is for your phone to access to the Internet. If you just normal people and doesn't want to know more, you should stop here.
Further question, can I use my desktop or notebook connect to the DiGi 3G services? The answer is yes. You can place your SIM card (with 3G service activated) in to GSM modem which support 3.G (eg. Huawei 160e), or you can use your mobile phone as a dial-up modem for your notebook, it works. The only thing missing is you will not be able to receive phone call while accessing the 3G services with your notebook.
How about the other way? Will it works if I place the broadband SIM card into the phone? According to the DiGi representative, it works as long as your phone support 3.5G services, but you can not make calls with it. Since I do not have a mobile phone which support 3.5G, I have not tested with it.
If you access to DiGi broadband web page, you will notice there are 2 data services call broadband and 3G, hope my explanation can help you to make your choice.