iMessage, SMS, and MMS

gnancy wrote:

I ‘ve been texting to another iPhone user - iMessage - blue bubbles. No problems.

Then, the texts changed to MMS - green bubbles with images.

(I understand it, these would have been sent as SMS if green bubbles with links.)

No settings were changed.

I’m not sure but does it have something to do with the recipient being in an area with…(I’m not sure) bad reception of something — cell, Wi-Fi, something else (not sure of what) ?

(And, I didn’t know what topic fit so I’m sorry if my choice was wrong)

You're assumption are correct, another thing could be that person imessage turned off. If you can't send or receive messages on your iPhone, iPad, or iPod touch - Apple Support