I am in australia with my uk sim roaming in slot1, and a local prepaid telstra sim in slot2.
I want a combination where the phone uses the uk sim for data, but sends sms and calls on the local telstra sim.
But if i switch data off on the telstra sim (whichever way round I put the sims in the slots) the telstra sim disconnects from the network.

If bth sims have data switched off, then both can work for calls and text.
If telstra sim ihas data active, then calls ansd text work from both sims.
if data is switched on on the uk sim, the telstra sim disconnects.

When i used two sims in uk with different networks this was not an issue. It seems to be something unique to the telstra sim. or there is a setting somewhere in the phone that is wrong.
Any ideas?

I'm finding the BV6000 a great phone by the way. I am using a live track app on it during a hang gliding competition.

Telstra have switched off 2G which is why there's no connectivity on your second SIM.