Is a FLASH sms stored on the cell phone? (those who appear on your screen and when you click OK" they disappear).
In fact it depends on the recipient smartphone.
For exemple on iPhone, if the recipient operator doesn't modify that Flash SMS, the SMS will appear
Full screen
without sender
and not stored
Antoine / Flash SMS Class 0
Flash SMS Class 0 on iPhone
Commonly Class 0 flash messages are not saved unless the user does something. Usually the user closes the message thinking the message can be found in the handset messages folder or SIM. That action discards the flash message from live memory. However, if a user chooses to select 'save' whilst still seeing the message it is possible some makes and models may save the message.
I have a Nokia 6303 that can send flash messages. Some brand name models from Alcatel and Phillips I recall forced the user to decide what to do with a text message on the screen. This was because cheap-end-of-market-phones (particularly PAYG) used SIM card for storing messages to counterbalance a low memory storage chip in the handset.
I will run some tests with the Nokia 6303 test handset that allows sending flash messages and see how some Samsung (Android OS) phones and some proprietory OS cope with flash messages.
Maybe someone else may care to try on iPhones or another brand name.
It will be interesting to see how the tests contrast with GSM standards such GSM0338; GSM0705; etc.