My absolute, must have, app for the N97 has now been revamped and is available signed.
Free-iSMS is an iPhone-like threaded text app that allows you to view a contacts conversations in order rather than skipping between Inbox and Sent.
Nokia were developing something similar for 3rd edition phones, called Conversation, but nothing has happened on that for over a year and it's not available for 5th edition handsets.
Free-iSMS has been around for awhile in an unsigned free version and I jumped on it straight away. It was fairly basic and only offered threaded text messages and not MMS's but it did the job.
The new version, Free-iSMS Business edition, contrary to its name, is not free. It costs 9 � or 12$ but is, IMHO, money well spent and something the Ovi Store ought to be offering.
It now offers support for, kinetic scrolling, MMS, contact thumbnails (where available), method of notification, skins and is much more integrated with loads of extra settings. You can set the way it notifies you about new messages, traditional, iPhone-like or it can open the message automatically (saves a lot of fiddling but not recommended if your boyfriend/girlfriend texts when your wife/husband is around). Oh, and it installs on E: or F: as well, which is a bonus!
You can watch the video here:-
http://www.youtube.com/watch?v=hOqpX9dTyHg
or to buy you will need your imei no: (*#06# on keypad) and email address. I received my 2 applications (app and keycode) back by email in 15 mins (although you are warned that it can take up to 24hrs.). See here:-