Hello,
Thank you for contacting our support team.

fring is not officially supported on the N900. The version should be out soon.

However, if you'd like to try out the Alpha version you can do that by enabling the Maemo extra catalog on your N900 and install fring through this repository.
You can find more details here:
http://mynokiamobile.org/2010/02/01/...ur-nokia-n900/

I'd like to emphasize the fact that the version is still for testing purpose only. If you don't feel comfortable enough to do that we advise you to wait for the official release.
We will not be able to give any support for this version.

If you have further queries, please do not hesitate to contact us again.

Thank you,
Dafna
fring Support