Text messages, now you see, now you don't

Are the real SMS messages carried by your network's SMSC, or Apple iMessages? I don't have an iThing so don't know how you'd tell (I have a vugie recollection some are green the others are blue) even if they hadn't disappeared. Can you disable iMessages?

The first was a message via Imessage, the second via the normal mobile network.

iphones don't send just normal SMS texts, the imessages can be deleted.

Blano explained on 07/08/2015 :

What, by the sender of the message?

The second message - might it have been sent via Imessage (hence her being able to delete it), but when I replied, despite having Imessage enabled and my phone connected via wifi, my message in reply went via the mobile network?

Might you have several iphones/ipads/ipods signed in on the same apple account, and they're being read and deleted on one just as they're being seen on the other?

Yes, for just that situation where you send in error.

The system can be a bit quirky like that, particularly when it decides that the receiver isn't currently available and so sends it via SMS.

Andy Burns was thinking very hard :

No, I am on my own and I only have one phone able to use the wifi here. The brief messages which saw, seemed to fit with the message thread and the message I had sent, even with my name mentioned in one.

Yes, I remember your recent threads.

The other device might not necessarily be on your WiFi, as long as it's on the internet somewhere. I wondered if your partner used to have another ithing on an account which you shared, and which has now been given to a relative?

Andy Burns formulated on Saturday :

No, she struggled to use just basic phones - but one relative does have an Iphone, which is set up for access on our wifi. I wasn't messaging him at the time, but his sister, when I saw a message asking who I was and a reply which mentioned my name, before both messages disappeared.

Anyway, the rule would seem to be - to leave messages a while before replying to them, to make sure they are actually valid and intended for you.