I just discovered my iPhone 4 will let me search deleted text messages. Is there any way to permanently erase texts?

What iOS revision are you on? As I recall, this was fixed in either 4.1 or 4.2.1? (EDIT: I was wrong, this is still an issue with how iOS handles the spotlight cache as of 4.3, and there is no non-JB way to resolve this on a stock phone with stock firmware)

That said, once jailbroken, you can actually just delete the SMS history database -- but that will delete ALL texts. Alternately, you can download the file to your PC and use an SQlite database editor to remove the offending text messages permanently. I think you have to compact the database after removing though, to ensure that the removed data is actually out of the file. Don't quote me on that, I'm not an SQLite database guru.... (EDIT: No compacting is needed, upon further research. Just clear the offending entries and re-save the file.)

Once you have removed the offending SMS messages from the SQLite database, you will need to clear the Spotlight cache on the iPhone, the easiest method for doing this is to SSH into the phone and delete the contents in the following directories.

/private/var/mobile/Library/Spotlight/com.apple.MobileSMS
/private/var/mobile/Library/Spotlight/com.apple.SpotlightTopHits

Until you delete the files in the two directories above, your SMS messages will still appear in the spotlight search results (as they have been cached into the spotlight search database), so if you only do half of the steps, you won't get the outcome you're looking for.

i have the same problem

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