Because I may want an always on instant connection? Because I may want to save my phone battery to talk? Because I don't want to mess with hotspot turning on or off? Because I value my convenience more? There's a couple of reasons. Otherwise the cellular versions wouldn't be selling out like they are.
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Well, some of us use our iPhones to, you know, talk. And I need my iPhone to last me a regular work day and then some, 10-12 hours. So yes, I worry about this aspect. I need my iPhone to work all day and be able to talk on it all day.