No. PayGo works fine on any phone. There's just a different tab to select the 4G PayGo vs the 3G PayGo when you replenish. If when you activate you do a "transfer" to the new phone from your old, your balance and number will follow along.
Your lucky you kept the 4s active since they stopped activating 3G's years ago. Just understand once you transfer to the SE, the 4s will never be able to be reactivated again.
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