Is it possible to switch it without having to activate it again? I'd like to be able to go back and forth.
If the Lumia uses a Nano SIM card, it can be switched. If not, you'll need to either cut down the SIM card or get a new one (no charge) and get an adapter to use it in the Lumia.
Also be aware that the Lumia and the iPhone require different data plans, so any time you want to switch phones you'll need to have your data plan changed.
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