Well about the battery issue. I had that problem once. It got so hot the the phone just shut off. The best way to fix it is using the stock voltage version of the kernel. That cleared up all my problems. Also you should be able to overclock higher. I use MIUI Android only because I am a member there and have been using there version since my Nexus One days.
Now about wifi calling it only work as long as you don't reboot. I have 2 G2x's and the same thing happens with both of them. Who knows. I don't worry to much about that anymore. Have unlimited minutes.