Perhaps when iOS 5 arrives this fall, it will offer a way to delete text messages en masse. Currently, your deleting options are limited in the iPhone's native texting app, which is disappointing to anyone with dozens if not hundreds of old text messages littering your inbox.
At the present, you have three methods to delete texts:
1. The fastest way to get rid of unwanted texts is to swipe on a message from the list on the app's home screen. A red delete button will appear; tapping it will delete the entire conversation. Unfortunately, you can't queue up multiple conversations for deletion but must go through one conversation by one.
2. You can also delete a conversation by opening a message and tapping the Edit button in the top-right corner of the screen and then tapping the Clear All button in the top-left corner. A large Clear Conversation button will appear at the bottom of the screen that will remove all messages in that conversation.
3. If you want to delete not an entire conversation but a specific message or messages, open a message and hit the Edit button. Then tap the small circle next to the message or messages you'd like to remove from the conversation. The circle will turn red with a small checkmark, confirming your selection(s). Then hit the Delete button at the bottom of the screen to remove specific messages. If you delete all messages from a conversation using this method, the contact name will remain in the list of messages on the app's home screen--handy if this is someone with which you text frequently and want to keep them in your recent messages list.