How to completely disable SMS and only use iMessage?

Unless you have SMS disabled on your account, you could still be receiving SMS and MMS from other people and AT&T would bill you for that. Perhaps that's what's happening?

So it's clear, the "Send as SMS" option under Settings -> Messages is NOT designed to prevent your phone from sending SMS messages in general (and therefore being charged by your carrier). It's a subset of all SMS sending - it's designed to only prevent sending SMS as a fallback, in a previously iMessage conversation, when the iMessage connectivity has been lost with the other party.

To my knowledge there is not a readily available option to prevent outgoing SMS completely on the iPhone. You may have to disable outgoing SMS from your number with your carrier (if they happen to support that option).

In your group chat, you might have been sending an MMS rather than an iMessage. This happens if some people in the group chat aren't using iMessage, as per the Android phone in the group you mention. See Apple's explainer of how group messaging works when some participants aren't using iMessage: https://support.apple.com/en-gb/HT202724

It's probably best to turn off 'MMS Messaging' (as well as 'Send as SMS') - this means that you won't be able to send or receive MMS. Here in the UK, this isn't an issue, as I don't know anyone who sends MMS - all carriers charge handsomely for the service at around £0.40 per message.

Apple's implementation of iMessage is quite confusing, because in a 1-2-1 conversation when sending multimedia, Messages can revert to sending an MMS instead of an iMessage when the connection is weak; but to prevent this in a 1-2-1 conversation, you need to ensure 'Send as SMS' is off, as opposed to ensuring 'MMS Messaging' is off for group chats. Confusing?!

A lot of people in the UK don't use iMessage to send multimedia to anybody - even in a 1-2-1 conversation - because they don't understand how to prevent the iMessage from sending as an SMS/MMS. This means that they start using WhatsApp to send all of their multimedia, and eventually it becomes their default messaging app, which is a shame.

iMessage would gain more traction here if Apple shipped iOS and its updates with the 'Send as SMS' function turned off by default. It's too confusing for the simple folk who just want to pick up their iPhones and start texting without incurring unexpected charges.

that would be something you have to talk to your carrier about.

AT&T can block SMS entirely. It doesn't sound like that's what you have had them do. If they had, you wouldn't be getting any SMS messages.

Does your bill break down messages by sent and received? Is that how you know that you're being billed for messages sent?

I am also experiencing this problem. A few seconds after tapping on the blue send button, it turns green and sends as a chargeable SMS, even though I have "Send as SMS"=Off. It seems that this setting has an effect only if there is a connectivity problem between the iMessage server and the recipient, not if there is a connectivity problem between the sender and the iMessage server. I have reported this to Apple, but all they could suggest was Reset Network Settings, which you say you've already tried.

I'm considering cancelling my unlimited family texting and making the selections you've suggested as I plan to start using an app called Viber. It's free and works over 3g or wifi but you have to interact with another Viber user.

I'm tired of paying $30 a month when most of my texts are family and close friends, They're going to have to use Viber or simply not text me.

Two and half years later this part is still impossible whilst on a cellular network, correct?

lenkun wrote:

.. I ONLY want to send using iMessage and don't want to send or receive any SMS messages at all ...

That is, via Settings>>Messages>>Send as SMS <off> you can ask your iPhone to not send SMS, but you cannot ask your iPhone to stop receiving non-iMessages.

Very recently, I actually started getting charged for SMS messaging with Verizon.

When I first got my iPhone, and then iPhones, I was very explicit with Verizon that I did not want SMS messaging and that I would not pay any charges that they ever tried to bill me. I was informed by the, admittedly shocked, CSR on the phone that it was possible to block messaging on their system, and that it would not be possible for me to send or receive SMS messages . . . caveat emptor - except for the ones that Verizon sent to me from their system, for their purposes.

So, naturally, when these charges began showing up on my bill after the recent upgrade to iPhone 6 for both lines, I was a bit confused. The first month was only two message charges. I double-checked both iPhones to ensure that the magic little Send as SMS button had not been somehow re-positioned. I called Verizon and explained to them that I did not use SMS at all and that I had confirmed that the aforementioned button was properly set. They graciously credited my account for a $1.00, the smallest CR they could issue.

The next month, another $6.95 worth of SMS charges showed up on the bill. This got me considerably more worked up. I saw the next stop along this path at somewhere north of $50.00, which might have been doable given my partner's propensity to send text messages over having live phone calls, but I digress.

I rechecked both iPhones again. Send as SMS button still in the NO position, however, all of the suspect messages (both received and sent) were in a Group Chat. The three participants in the Group Chat were - my iPhone with 'Send as SMS' set to off, another iPhone with 'Send as SMS' set to on, and an Android phone. The Android phone began the Group Chat, the iPhone with 'Send as SMS' enabled sent the first response, my iPhone received both and somehow was able to respond into the Group Chat, sending an SMS message to both recipients.

Today, I had the time to log in to the Verizon portal and poke around a bit. I was at it for about five minutes when I happened upon a remote page that held the Verizon end of the magic checkbox Block Messaging, which dutifully and somewhat counterintuitively explains that ONLY SMS messaging (Video, Text and Picture) will be blocked, even though the ominous feature name conveys a rather confusing totality.

Once I rechecked this box, I called Verizon and explained what I had found. I also voiced my suspicion that this likely happened during the iPhone 6 upgrade process because it was after that when the problem began. The phone rep went and immediately processed a CR for the charges and informed me that the taxes will be computed off of the bill next month.

As a final test, I waited about 10 minutes and attempted to send a response into the Group Chat that seems to have been responsible for this incident and it no longer works. Problem solved.

I do believe this does point out either 1) a bug; or 2) an incomplete implementation of turning off 'Send as SMS'.

Hope this will be helpful to someone else.