If you look at the fortreess website you will be able to find "real" dual sim phone. That would be the best bet in IMHO as they come with warranty and have real software ( not some hacked kind).

As far as the plan you talk about im not to sure what you mean but it may be something that is offered by China Mobile (which also operates in HK) you get two numbers. One for HK and one for the mainland yet it goes to your same sim