In the settings for the iOS 5 Messages app there is an option to send messages as SMS "when iMessage is unavailable". Under what conditions is this the case? Is it merely the obvious (no data connection available or the iMessage server is down, or the message sits undelivered for a time), or is it more subtle (for example, the service simply not having had time to confirm that the recipient has iMessage enabled, or that the recipient's device cannot be contacted at the time of sending)?

Phrased another way: what are the conditions under which an (intended) iMessage wold go undelivered, and are there other events that would cause a message to be delivered as an SMS?

  • I have iMessage set to on. Late last week, I sent and received about 50 text messages to other iPhone users. When I checked my Verizon account every text that I sent/received was charged against my monthly count of 250. I need to verify that the other people had iMessages set to on. Commented Dec 19, 2011 at 13:51
  • you just had to enter the person phone number and wait (like 10-20 seconds top) to see if the header switches from Message to iMessage to know if they have iMessage activated. Commented Dec 19, 2011 at 13:53

8 Answers 8


It means either

  • when the device is unable to determine if a message has been delivered over the iMessage transport successfully. When a successful delivery occurs you see a little 'Delivered' notification below the message in the history, and after a period you should have the option to resend as an SMS

  • or the recipient has no registration with the iMessage server to indicate that it could use the iMessage transport and will use SMS instead.

  • Is the first case ever automatic, or is a confirmation always required?
    – orome
    Commented Nov 3, 2011 at 21:51

Another scenario I've discovered is when I'm connected to a WiFi signal that requires HTTP authentication. If I bring up the browser and authenticate, I'm fine. However, if I just let the iPhone connect to the WiFi, but I don't bring up the browser to authenticate, then the data network will be seen as dead, and any iMessage attempts will fallback to SMS (green dialog boxes). But then, as soon as I bring up the browser to authenticate, my conversation will switch back to iMessage (blue dialog boxes). So unless I remember to keep re-authenticating to the wireless network with the browser, my best bet it to just "Forget this network" and allow the iMessage to be sent over the AT&T data network, then it will remain as an iMessage.


An example of a failed iMessage: I do not have a data plan. If I send or am sent an iMessage, and I happen to walk outside of the Wi-Fi point I'm connected to, it can fail to send, forcing me to then send as SMS.

Hope this helps.


iMessage uses an internet connection to send a message to another Apple device, if you do not have a 3G data plan or internet connection it will not work, that also goes for the person who is receiving the message, if they do not have a connection it will fail to deliver.

I know someone with a 3G without a 3G data plan (dont ask) and in order to send a SMS you will need to double tap the sent message and choose 'send as SMS'


My understanding is that what this setting controls is the choice between SMS and MMS when iMessage is unavailable. Apple has a support document iOS: Using Messages that says

On iPhone, if iMessage is unavailable, the message may be sent as SMS or MMS, depending on content. Carrier messaging rates may apply. You can adjust this behavior in iPhone at Settings > Messages > Send As SMS. Messages sent using iMessage appear in a light blue bubble, while messages sent using SMS or MMS appear in a green bubble.

So, as I interpret it, if you have this setting off, then a message that can't be sent via iMessage may be sent as either an SMS or an MMS. If you turn the setting on, a message that can't be sent via iMessage will only be sent as an SMS.

  • The question is: what does "can't be sent" mean in this context.
    – orome
    Commented Nov 30, 2013 at 14:23
  • In this context, "can't be sent via iMessage" means just that: the message can not be sent within iMessage, for example, if the recipient has disabled iMessage or is out of data connectivity.
    – jetset
    Commented Dec 7, 2013 at 22:17

@Kristy, you are confusing a few different things. To clarify:

  • iMessage sends messages (not necessarily SMS texts).
  • iMessage is capable of sending messages in three ways: within iMessage, as SMS text, and as MMS messages.
  • iMessage attempts to send messages within iMessage. This is only possible when you have enabled iMessage and are sending to recipients who have Apple devices with iMessage enabled.
  • When a message cannot be sent within iMessage, it might be sent as an SMS or MMS
  • If the message has multiple recipients or contains attachments (such as pictures or video), iMessage normally sends it as as an MMS since it exceeds the capability of SMS
  • If you set the option to send as SMS, that tells iMessage to not send it as MMS

Here are some reasons why you or your recipients might either prefer or want to avoid sending messages within iMessage or as MMS:

  • iMessage uses your data service
  • SMS is its own service
  • Depending on your cell service company (carrier), MMS may be its own service or might use your data service

iMessage is not really free but rather, because it uses your data service, it depends on your data service package. There is no special or secret "deal" between Apple and the carriers specifically for iMessage.

  • Some cell plans have monthly data caps, while others offer "unlimited" data. Even with "unlimited" data, usually data usage over a certain amount is throttled down to lower speeds.
  • Some cell plans charge per each SMS, others have monthly limits on SMS, while some have unlimited SMS
  • MMS may be charged against data usage or may have a per-MMS charge or may come in blocks of MMS

So, if you or your recipients have a cell plan that offers, say, unlimited SMS but capped data, you or your recipients might prefer to disable iMessage and use SMS instead. Or, if you have an unlimited data plan and pay a per-SMS charge, you might prefer to send as much as possible via iMessage. Even with an "unlimited" data plan, if you use enough data to be throttled down to lower speeds later in the month, you might prefer to disable iMessage. Or you might enjoy the extra benefits of iMessage and keep it enabled.


Okay peeps, listen up! iMessage is an IOS 5+ ONLY software that sends sms texts between 2 or more IDevices that BOTH have IOS 5+. It uses your cellphones internet connection to do this. If iMessage is enabled, and you send a message to another user that has IOS 5 or IOS 5.1, the message will show up on your screen colored blue instead of the usual green color of texts (Note: This is a good way to check if iMessage is working, as well as a way to check if the person you are texting has IOS 5)

Now for the perks of iMessage. When using iMessage, all texts sent using this feature are completely free through a deal Apple made with AT&T, Verizon and Sprint (Altough Sprint is like a secondary company, so if you are using google voice, and have a different number on Google Voice then your actual cell number, iMessage MIGHT be disabled) so if you bought an IPhone, and are using a SIM card from a different company, well, tough luck I guess. There IS a reason why only SOME companies sell Iphones you know.

When using iMessage, if you leave the screen on the messages app, waiting for the person to reply, it kind of has a Skype-looking feature, that whenever the person is typing, you will actually get a "dot dot dot" (...) on the bottom left, right above the keyboard.

The option in settings to send messages as SMS "when iMessage is unavailable" simply means if you are using the Sprint/Google Voice combo mentioned above, or if the person you are messaging does NOT have the IOS 5+ software (meaning they can NOT receive iMessages) then the phone will send a normal text message (carrier rates apply).

Hope this helped out. If I figure out anything else, I'll edit this later.


On iPhone, if iMessage is unavailable, the message may be sent as SMS or MMS, depending on content. Carrier messaging rates may apply. You can adjust this behavior in iPhone at Settings > Messages > Send As SMS. Messages sent using iMessage appear in a light blue bubble, while messages sent using SMS or MMS appear in a green bubble.

The above comes from Apple's support article.

  • The question is: what does "when iMessage is unavailable " mean?
    – orome
    Commented Dec 20, 2013 at 22:52

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