The only cellular phone provider that retains and keeps the content of your text messages is Verizon Wireless but they only retain the content from the text messages for up to 5 days before it gets overwritten and is lost forever.
Call details however are kept much longer as in up to a year or more and for some cell providers they keep the call detail records for up to 7 years but for the text messages they're only kept for up to 5 days maximum.