Dual SIM Switch Widget is the first free app on Google Play that gives us ability to toggle our SIM cards on and off, using simple widgets on our home screens. It does similar job for mobile data.
You can also schedule this dual SIM toggle. For example, you may want your SIM1 to turn on at 9 AM and turn off at 5 PM automatically, and to switch data accordingly, without user interaction. It can be set to skip weekends, too.
<b>Limitations</b>
The app is not universal! It was designed for <i>most</i> dual SIM phones based on Mediatek processing units, such as some but <i>not all</i> models of: HTC, Alcatel, LG, Huawei, Sony, Lenovo, Prestigio, Gigabyte, ZTE, Acer, BLU, Archos, Philips, Micromax, Cubot, Intex, Panasonic, Gionee, TCL, Xiaomi, Oppo, Karbonn, Meizu, XOLO, etc. If it doesn't work on your dual SIM device, please let me know.
<b>Further development</b>
Originally, I made this app for myself. If you have a suggestion for improvement on a working app, please post it by e-mail or as a review, but I can't guarantee neither response nor commitment to it.