iMessage on two phones

Hi everyone,

Please can someone help me with this issue?

I have an original iPhone SE and an iPhone 8. The SE is my old phone and I am preparing it to be a backup phone incase the 8 ever breaks.

I am trying to turn on iMessage.

On the iPhone SE, the messages will send through my email address but my phone number is greyed out and says 'waiting for activation' as it has been for over 24 hours. The phone is connected to wifi and has an old deactivated iD mobile SIM card.

iMessage is working on my iPad which has no SIM card in at all so I presume this is possible?

Thanks in advance

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