[ViViDboarder]

How do you know this? Is this old?

I have a few Google Fi data only sims and as soon as I put one in an iPhone, iMessages to the original sims number stop going through at all.

I remember there used to be issues like this when people switched to Android. Though this could still be an issue and maybe inserting a sim with a different number causes Apple to automatically unregister the original number, but just moving the sim does not.

[chrischen]

I guess this is technically by design, but only if you have your iCloud account associate the number with iMessage (you toggle the send/receive from the number in the settings).

So even if your phone isn't using imessage, if your computer or ipad is, they'll receive the imessages and apple doesn't also send a text in addition to the imessage for the non-Apple device.