SIM services menu is a really important feature that is missing N900.

Many provider services are in there and cannot be used in other ways. For example, I have 2 numbers (lines/connections) in 1 SIM card with Vodafone Greece, called Vodafone 2gether.
To change from one line to another you have to go in that menu and select the appropriate choice. (all Greek providers have this service with the same way)

It is necessary to be added soon in an update.

Ya this is like one of those basic features we took for granted, a lot of services and information can be retrieved/changed using the SIM toolkit. I think this will be implemented when the service number dialing ie. *# commands are implemented.

You should file a bug (eg https://bugs.maemo.org/show_bug.cgi?id=5356), so that people can vote (https://bugs.maemo.org/votes.cgi?act...5356#vote_5356) on it. The more votes, the more the developer of that particular N900 subsystem will focus their attention. You might even want to add a link to the bug to your signature in this forum, so that every time you post you can "campaign" for it.

You will have to set up a different account on bugs.maemo.org,

there already is a bug.

This has been reported in several ways, including aki no maemo.org
http://talk.maemo.org/showthread.php?t=38516
http://talk.maemo.org/showthread.php?t=37703
http://talk.maemo.org/showthread.php?t=35829
http://discussions.europe.nokia.com/...thread.id=1809
https://bugs.maemo.org/show_bug.cgi?id=7424
https://bugs.maemo.org/show_bug.cgi?id=6614
let's see what solved later.

OK, but there is no solution. Here is the brainstorm link http://maemo.org/community/brainstorm/view/sim_toolkit/