Having worked for the largest cellphone manufacturer (take a guess) I can tell you that yes indeed everything ends up on some server... actually more like 2 servers. SMS text messages are handled by a completely different server/computer/whatever and everytime you send a message it groups it under "originating" area code, the second, 3rd, 4th, 5th, & 8th character of your ESN, time/date of sent message, #of characters (up to 160 - may be different now), route of message, something caled a ECE or EEC Header and finally the message itself. now after all of that there is a logging number assigned to the message itself, the sender address gets a logging number, and when the message is received and "opened" it sends a signal back and attaches a 6 digit alphnumeric "ID" tag to the end of the ECE or EEC. Phones with SIM cards actually store 8 160 character messages if you go into its NAM programming.
if all of this sounds too confusing I can sum it up for you: they know everything :[ voice data I have no clue though.
cheers,
-Aja909-