Why are you do sure 4g is going yo cost extra, most other carriers dont charge extra for their 4g, even if its much faster then any capother the public just sees 4g as 4g. The way I see it is they are probably going to go to a tier system for 3g and 4g will just use the same data cap. As far as battery life 4g doesnt burn that much more then 3g and you can turn ot off when you need to. The battery life problems on the tbolt are a fault of its tiny battery , and thats why the stock bionic battery is pretty massive. On my tbolt I ended up just getting an extra battery and I keep 4g on all day without a problem ive gotten some days without needing the second battery.
