Soon Microsoft may release stand alone Smart dual SIM application for Windows 10 mobile devices, as the internal app link has been posted on the twitter. It is clear that it will be available for only dual sim devices. You can install the app now on Windows 10 Mobile devices by using the link below though it still has not been released officially by Microsoft.
Customise your Microsoft Lumia phone experience with this helpful app, found under Settings in your phone.
Thanks Gustave M for this tip!!!!
[appbox windowsstore 9nblggh2jxj3]