One of my favorite features of Gmail is how it's emails are threaded based on contacts and subjects. I believe that Blackberry devices have a similar SMS system. Nokia is developing a freeware application called Conversation which gives you this functionality on the Nokia E71.
According to the Nokia page,
Conversation is a messaging application that allows you to follow your message conversations, which it organizes into threads with individual contacts. The application also makes it easier to reply to messages and continue with conversations.
After installation, the application will appear in your device as an application shortcut, and as a new tab in your Contacts application.
Right now there is no version for the Nokia E71 officially supported, but I have the E90 version installed and it works fine. I haven't seen any glitches or problems at all. You can assign it as a shortcut on your standby screen. I have mine as the long press email key which works great with my setup. The email key takes me to the email application, and if I hold it down for 2 seconds it takes me to the Conversation application where I can read all my text messages.
I hope that someday Nokia implements this as the default messaging application but it doesn't. However, when you open a message in Conversation it will be marked as read in the default messaging system. Another quirk is when a new text arrives and you want to click the notification to read it you will be taken to the default message app. Now I just end up going straight to my Conversation shortcut.
Have you tried this application out yet?
Click here to install Conversation on your Nokia E71. Make sure to follow the instructions and download the E90 version.