I've noticed there are problems on how RR manage incoming call in z00a phones.
You can't switch between two incoming phonecalls.
In the native rom, you can able to pause in order to answer the incoming call from another line.
Another issue is that while you are on call n sim1, and you want to make another call from sim2 you can't able to do that.
Another issue is when you are in tollfree call and you answer a second call for the same sim, when you've finished the second call you can't continue on the first call, you have to hang it up and make a new call.