Default [Q] Supports simultaneous operation of GSM and 3G MT6589

For example Sony Ericsson starting from not smartphones may work in this mode, even on the single SIM.
But with chinese Android 4.2.1 I can not use the internet connection from the first SIM during a conversation from the second SIM. Why?
Is it system issue? Or MT6589 baseband not support it?

UPD: Most phones(include SE seeing up) can work simultaneously with the conversation and the internet connection via the 3G network. But simultaneous data transfer with both GSM and 3G may not be established, probably due to too much frequency separation of these networks.

But I want to know about the possibility of work in this mode with dual sim high cost or other models.
Please reply!