No you don't have to change your plan. I've been with Verizon since 2008 and my mother has for even longer and she still has the old unlimited data plan where they dont throttle your usage after 22gigs (theycall it a grandfathered plan). I would expect customer service to offer you a new plan as the company is always modifying service plans for maximum profit. I kindly decline when offered to me.
I just purchased two Galaxy S20 I did not have to change my plan and I am with Verizon.
I don't think so but you can call and ask!
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