Changing default SIM card for data connection?

[Dosc]

maybe this helps:

Enable 3g on both sims?

With tasker app and mtk control plugin you can create a task that switch with one click 3g from one to the other sim card. I use this to enable my data-simcard with 3g, when I need data.otherwise 3g is enabled on the phone simcard to have a better connection.