There's a simple solution.
If you need simultaneous voice and LTE data, then don't buy an iphone. It wasn't designed to meet your needs.
If you're ok with simultaneous voice and 3g data, and insist on getting an iphone, you're stuck with ATT.
Rather than complain about what the iphone can't do, just buy a phone that does what you need it to do. Problem solved.
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Exactly. Or carry 2 phones, or an iPhone and iPad, is yet another option. solve the problem, don't bitch about it.