Here it is a year from the original post, and the problem still persists?
In scouring the forums here it seems that this problem is only plagued by HTC phones. I did a simple search for " slow deleting text " and the only users seem to be HTC users.
I have a droid Incredible, it has 8GB of internal storage, and a 1 GHZ processor.
1) my dumb phone could delete 220 text messages in less than 10 seconds.
2) It takes my HTC Incredible 10 seconds to delete 15 messages, that is .7 seconds per text message.
I find in unreasonable for such a fast processor to have such issues with such small amounts of data, resulting in force quits, and not being able to use the device.
I believe that having to do a hard reset on your phone constantly is also unreasonable.
My colleague who has a Droid2 does not suffer from this issue what so ever, and in hearing that and the simple fact that a search on this forum seems to show its HTC users only.
I do not think that it is unreasonable to have thousands of text messages on phones like this. It is 2011 not 1999. As pointed out above the iphone could delete thousands in just a few seconds.
Welcome to HTC sense UI - I believe the problem lies with this in my opinion.