Please understand that you are Not talking to Apple, Inc. when you post here. Responders are almost exclusively other Users like you, who volunteer their time to answer User queries. Apple does provide network Hosts who help keep order. They insist that Politeness and Respect for one another prevail here.
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We have two sons, one has iPhone, the other has Android. The messages sent from Macs or iPhones, to iPhones always seem go right through, without hardly ever a problem.
The messages that have to be converted (by passing through the physical iPhone onto the cellular network, as described in the articles cited) to the SMS message system work rather badly by comparison. Surprisingly often, we get a notification that the message did not go through. When that happens, we typically resend the message. We frequently get reports from our son that "you sent the same message twice". When we try to attach pictures (almost never a problem when going to an iPhone) they sometimes go through with the message, sometimes not.
Compared to the IPhone message system, my impression is that SMS message system:
a) works somewhat haphazardly.
b) does not play nice with iPhone messaging.
^-- THAT sort of information is stuff you can not get from Apple support, and what makes posting on the forums special. But if you want to ask to Apple support, and they say they are not available, then call back another time.
