MMS has groups but imessage and the new android messenger don't use MMS when everyone in the group has the same OS.

So when you switch OSes you get kicked out of the group.

For some reason there are a number of people on hackernews that are really struggling with this idea and I'm kind of surprised it's so difficult to understand. I thought the last guy I talked to was just particularly dense but maybe I'm failing to communicate it effectively? Maybe it's harder to understand than I thought it was? I'm not sure.

My experience with iMessage has been that the group text continues to function as an MMS group if a member switches OS, even if it was an iMessage group beforehand. Or sometimes someone even sends a one-off MMS at a time that they have cellular reception but no data, and the messaging app still seems to know which group text to put it into.

So I guess my experience is that you don't get kicked out of the group.

To be pedantic MMS has groups, not SMS. A distinction I recently discovered when switching to the pinephone which curreently supports the latter but not the former.

mms are also often not included in flatrates and riddled with security problems. noone i know uses them.

no.

what you have probably mistaken for is send to multiple destinations and reply-all.