I dropped my original phone and ended up using a basic Motorola as a temporary replacement. My mom sent me her old (but nicer) phone, so I switched my SIM card over to it. Just the other day, I sent a picture of my dog from my active phone, and I didn't get a response. But when I powered on the Motorola today, it had a text message from someone replying "so cute" to my dog pic that they sent on Wednesday! How could that happen? One thing to mention is that the Motorola is running Android, while my original phone was a Galaxy S9 and my current one is a Galaxy S10. The text said SMS/MMS, but it also indicated "please insert SIM card to reply." I do know the Motorola is connected to Wi-Fi. It only got two texts from the same person, and this hasn't happened before since I moved my SIM about two weeks ago.
7 Answers
Make sure to clarify whether this was an SMS message, an iMessage, or from a different app. It feels unusual only if it was SMS and not an app-based message.
Was your original phone an iPhone? If so, iMessage doesn’t rely on a SIM at all. You might need to disable it in order to get texts on your new phone.
Could your old phone be using an e-SIM? Also, is the Motorola connected to the Wi-Fi? That might explain why you received the message.
Was the text from an app like WhatsApp or Telegram? If so, it may still be linked to that phone because it’s logged into the network there.
I checked the text app on the phone, and it shows "SMS/MMS" as well, but since it demands a SIM card, I’m not sure how it worked.
Just a thought—are you sure you’re not experiencing some sort of confusion? It’s important to rule out anything strange happening at home.
Lol, I know I’m not hallucinating! If I were, my bird would definitely be acting weird too, right?
It’s possible for SMS to come through via Wi-Fi depending on your phone’s settings, which may explain the text you received.
If Wi-Fi calling is turned on, you can still receive SMS texts even without a SIM in some areas. That's likely how you got that message.
I think that's what happened too, but it's strange that it only got this one text string. I can't send messages from it, though; it won't let me.

It said "SMS/MMS" below the message, but I can't reply to it because it asks for a SIM card. Still, I'm puzzled why the message would go to the Motorola first.