For example, if I get promo code which is 15digits of letter. I have to do as below.
1. long press the MMS which is including promo code.
2. choose new message on the option bar, and then whole text will be pasted in the new MMS writing mode.
3. long press promo code in the MMS and copy it to clip board.
4. if press back button, MMS will be saved and I have to delete this new MMS. or long press again in the MMS writing mode and choose all texts in the MMS and delete it and the press back button.

as you noticed as above, it is very difficult to partially copy within the long texts. If TEXTRA apply partially copy function, it will be wonderful for me.