The iPhone's built-in SMS application does not allow you to forward a SMS message. To do that you need a 3rd-party application, WeTool, that you can get through the Installer module. Once you've installed it, launch it, go to the "Text Log" view, select the message you want to forward, click More at the top-right corner, and finally click Forward.

The iPhone's built-in SMS application does not allow you to delete a single SMS message, you can only delete a whole conversation/chat/discussion, which is something you don't generally want. To delete an individual message install WeTool through the Installer module, and launch it. Now go to the "Text Log" view, click the Delete button on the top-left corner, click the Stop symbol on the left side of the message you want to delete, and finally click the Delete button on the right side.

When you are writing some text on the iPhone (any application) and you need to add a punctuation char (comma, semi-colon, full stop etc.) you generall tap the "123" button, tap the punctuation char, and then tap the "ABC" button to switch back to the normal keyboard mode.

There's a quicker way to do it though: press the "123" button and -- while you hold your finger down -- drag your finger on the punctuation char. When you release the finger the punctuation char will be added and the keyboard will still be in normal mode.

If you are writing a SMS or a mail (or some other text, in other applications) and notice you must go back to edit or correct something, it would be helpful to precisely move the caret back to that point and make your correction, without deleting all text written so far. To do that, tap and hold your finger on the word you want to edit, or somewhere near it; after a couple of seconds a magnifying glass will pop up allowing you to move the caret forth and back one character at a time by dragging your finger.

To type an accented letter when writing a SMS (or while writing text in any other application, for that matter) press the un-accented letter and hold down your finger until it shows the accented variations; then drag you finger over the accented letter and release it.

iPhones with firmware 1.1.3 or previous versions may show SMS messages of the same chat in a wrong order. Upgrading the iPhone to firmware 1.1.4 (via iTunes) fixes the problem. Note that iTunes automatically backs up your data before the update and restores it afterwards, so no data (SMS, call list, contacts, music, videos etc.) is lost in the process.

Attention: if you're using an unlocked iPhone, the firmware update will re-lock it. You'll  need to unlock it again after the firmware update.