Ok, to explain the pinging, ponging, SMS (Short Message Service) and Smartphone 'Messaging' goings on, lets have a scenario or 3.
We have;
Person A, iPhone with iMessage
Person B, iPhone with iMessage
Person C, Blackberry with BMM
Person D, Nokia C1 (basic mobile phone)
Scene 1;
Person A wants to text person B.
When person A wants to text Person B, A will open the message app and pick B out of their contact list. When iMessage senses this, it pings B's phone to see if that phone is connected to the internet (3G or wireless). If it is connected (and is running iMessage), B's phone will pong back and say it is connected to the internet and running iMessage, and the msg will go by iMessage, if not it will go by SMS.
A sends B the message. If this is by iMessage, A will get a notification that it has been delivered, ping pong. When B reads the message by opening the 'message app', B's phone pings A's phone and tells it that the text has been read. When B starts to reply to A's msg, B's phone pings A's phone to confirm the delivery method (iMessage or SMS) which also informs A's phone that B is replying.
B then sends the msg and A's phone pings back, which tells B's phone the msg has been delivered. Not until the conversation is opened, does A's phone ping B's to tell it that the message has been read...however, as earlier discussed, the text of the msg can still be read without opening the app and in turn not activating the 'msg read ping'.
Scene 2;
Person A wants to text person C.
When person A wants to text Person C, A will open the message app and pick C out of their contact list. When iMessage senses this, it pings C's phone to see if that phone is connected to the internet (3G or wireless) and running iMessage. C's phone is running BMM and as it is not compatable with iMessage, A's phone will not get a pong back and the msg will be sent by SMS.
On receipt of the message, C's phone will try to send the delivered ping to A's phone, but because the 2 messaging programmes aren't compatible, no delivered or read pings are sent, (which would have happened if A had a Blackberry as per the 2 iPhones scene)
C begins to compose a reply, C's Blackberry sends a method check/writing ping but it isnt registered on A's phone as the systems are different. C replies to A's msg by SMS.
Scene 3;
Persons A,B or C want to text person D and/or D wants to text A, B or C.
Because D's phone isn't 'smart', all messaging is carried out using SMS. D's phone does not ping or pong, however when A,B or C reply to D's msg, their phone will send a ping to see if the msg can be sent by their messaging system.
However, despite not being smart, D's phone can still show a message's text, without opening the 'text app'.
The various networks will not only have copies of all messages sent over the last up to 7 years from that persons contract/number, but also a record of all the various method of delivery, reply, delivered or read pings.