So...
even with a patched libsms the errors are still happening and the N900 discards the received messages...

Someone would try?
Pick an android phone and send to an N900 the following emoticon:
http://emojipedia.org/lg/g4/baby-angel/

That should correspond to:
http://www.iemoji.com/view/emoji/100/people/baby-angel


The result:
sms-manager[]: GLIB WARNING ** default - Error decoding TPDUs. Discarding message

WITHOUT ANY notification.

At the moment i'm trying to get at least a message about this using a dbus-script:
/usr/local/bin/incoming-sms.sh * * Phone.SMS IncomingSegment