Sending fullscreen, disappearing SMSs to an iPhone

Question

Where I live (Copenhagen, Denmark) there is a taxi company which offers to send you an SMS when the car you ordered is about to arrive.

The SMSs are unlike any I have received on my iPhone in that they appear fullscreen and are not saved to the SMS application. See this screenshot:

As soon as you press "Dismiss" the message is completely gone. No trace of it in the SMS application.

I was thinking that the ability to do this could be useful for apps in some way. Perhaps offered instead of a regular push notification for super important things. But most of all I am curious to learn what's going on.

• Is this a regular SMS or some sort of cell network alert?

• How can these be sent? Is it content formatting which triggers this special display or is it a protocol feature?

• How would they appear on other phones?

• If it is not a regular SMS but some sort of network alert would it be possible to send one to a 3G-enabled iPad?

Answer 1

Prefix your text messages with *go.

See this link!

Be sure to see this link (link is now dead so view the archive.org version) too as it may cost an additional charge to send them. After research only GSM providers over seas (not in the US) can do this.

Answer 2

I've just written up a blog post on these class 0 or "flash" messages here. They look slightly different now in iOS 7:

The SMS specification has this to say about class 0 messages:

When a mobile terminated message is class 0 and the MS has the capability of displaying short messages, the MS [mobile] shall display the message immediately and send an acknowledgement to the SC [service center] when the message has successfully reached the MS irrespective of whether there is memory available in the (U)SIM or ME. The message shall not be automatically stored in the (U)SIM or ME.

I had a look into the technical details of these a bit more and it turns out that the class is set using the last 2 bits of the "Data Coding Scheme" (DCS) field of the SMS-DELIVER and SMS-SUBMIT protocol data units. The DCS field is a single octet, the use of which varies depending on the value of bits 4-7. A message class can be specified in the cases where bits 4-7 are set to either 00xx or 1111.

In the former case, bit 5 indicates whether or not the text is compressed, bit 4 indicates whether a message class has been specified, bits 2 and 3 indicate the character set and bits 0 and 1 specify the class (if bit 4 is equal to 1). So, for instance, 00010000 (0×10) would indicate an uncompressed class 0 message using the GSM 7 bit default alphabet and 00110100 (0×34) would represent a compressed class 0 message with an 8 bit-encoded UD field.

Answer 3

It's called a Flash SMS, and works on other phones too. Source: http://en.wikipedia.org/wiki/Short_Message_Service#Flash_SMS