I have been using chinese dual SIM phones for quite some years now and love the facilities they provide. I can have both my work SIM and my personal SIM in one device rather than having to carry two phones around with me as I used to. Also using the dual SIM solution allows both SIM's to be connected to the hands free system in my car so that I can make and receive calls on either SIM through the car system.
However, there has always been a downside and that is the SIM management facilities built in to Android. When making a call or text, when you press the send button a box will pop up asking which SIM you want to use to make the call/text which you have to select before the call is made. There is a facility whereby you can assign each contact in your address book to a particular SIM but even this does not automatically make the call using the assigned SIM. All that happens is that when you make a call/text the same box will pop up asking which SIM to use and the only difference is that now there will be an indicator next to one of the SIM's recommending it based on the SIM assignment but you still have to manually select it. Now I don't find this a particular problem when using the phone normally but it is a major problem when using the phone via the hands free system in my car because when I make a call through the car system the box still pops up on the phone asking which SIM to use which is a big drawback and means that the phone has to be accessible and visible while in the car.
However, I have now found a great solution that I have been using for about a month now and is working great. It is an APP called 'MTK Control' which is available through the Google Play Store and is available as a free version and a premium version. I would suggest testing it with the free version first to make sure it will work with your phone but if it does work ok then I would wholeheartedly recommend purchasing the premium version which is only 79p (around $1) and adds additional functionality like homescreen widgets etc.
So, what does 'MTK Control' do that the built in SIM management does not. Well, everything to be honest. Firstly it gives you toggle actions to turn each SIM on/off or to toggle calls between the two SIM's and also to toggle the data connection between the two SIM's.
All of these functions can be added as widgets to the homescreens in the premium version as shown below.
However the best part comes with the ability to create rules to assign contacts and numbers to a particular SIM and have that SIM used automatically with no user intervention required. This is done in the following screen.....
….where you can input a single number, a group of numbers using wildcards, an individual contact or a group of contacts and then select which SIM you want to assign this rule to. So the following screen shows that the contact groups 'Family', 'Friends' and 'Services/Shops Personal' are asigned to SIM 1 (personal SIM) and the groups 'Coworkers', 'Customers' and 'Services/Shops Work' are asigned to SIM 2 (work SIM).
There is also an auto learn function that can be activated so that the first time you dial a new number or contact it will ask you which SIM to use but it will then automatically create a rule for this number so that in the future it will be automatically chosen.
The best part about this is that it works seamlessly with the hands free system in the car. When I initiate a call from the car system the phone will automatically select the SIM to use based on the rules that have been setup. This means that I don't need to physically access the phone at all and it can stay in my pocket.
In my view this app does what the built in SIM management should have done from the start. The developer of the app is constantly updating it with new features and is very approachable and takes on board feature requests.
One word of note, as the title of this thread suggests, the app will only work with Mediatek based mobile phones and will not work with phones like the Samsung Duos range etc. I personally have tested it with the following phones:
UMI X1S (MTK6589)
Jiayu G3 (MTK6577)
Jiayu G4 (MTK6589)
Jiayu G4S (MTK6592)
I haven't used the text or data functionality so can't comment on that specifically but the call related functions and the calling rules I use all the time and have worked flawlessly.
NOTE: This app is now called 'Dual Sim Control' and is now compatible with Samsung Duos phones as well as MTK based phones.
I have no connection whatsoever with the developer of this app. I am just a very happy user of it.