Have you tried activating Advanced Calling on the one that you can't talk and browse on? I thought I read if you do that and have 4G that you can talk and surf.
Honestly no...I also read that your call drops the second you lose 4g and drop back to 3g. It's bad enough not having the talk/data capability...I don't want to add dropped calls to the issue.
It's a feature you can enable and disable and it's free depending on the plan you have. Though if you are in a spotty area and switch between 3g and 4g, it wouldn't be a good choice.