Before you go through too much trouble, if you have an account with the same carrier, check your service agreement. It could be that they spell out in that contract how long they store SMS content. Many only have it for 72 hours, after which they delete it; which is probably useless for court orders and subpoenas. Be sure you know what you expect to find and that it will actually help your case. For example, even if you do succeed at getting a text that says "it was awesome having your big <edited> sliding up inside my wet <edited>" it does NOT prove that such a thing ever actually happened.
"Personal density is directly proportional to temporal bandwidth."