apparently (by a google search I learned that ) log and content of cell phone messages are kept for some time by the carriers (Depending on the carrier it could range from a few days to several months). and yes they can provide the content of the text messages only if they are subpoenaed and if they haven't already deleted them.
However they say the best way to go is actually subpoena the headset / cell phone used as it's possible to recover even deleted messages from a cell phone.
Really? But would there been any way of getting texts and voicemails that are 19 months old though?