I'm sure if the courts wanted a copy of sms sent to and from a certain cell phone account, there wouldn't be a problem with T-Mobile coming up with a full transcript of sms messages for a given time period (whatever it is that they hang on to them for or can get records of). But without a court order, as far a their response to end users is going to be, Nope not something we are able to do.
As for monitoring SMS to and from you own phones, other than making backups of them, as far as I know there is no legal way to do this. So if the question is, can yourself/girlfriend/wife/enemies find text messages after they have been deleted from the "target phone", somewhere in the net, or have T-Mobile send copies (electronic or hard copy) to them. Then the answer is nope.
UNLESS the SMS service you use, makes online copies of SMS, email, contacts and the like, automatically. Then you/they, may very well be able to get ahold of SMS messages, long after they have been deleted from the phone.