Apperently, modem-manager-gui requires that lib: /usr/bin/modem-manager-gui: error while loading shared libraries: libgtkspell3-3.so.0: cannot open shared object file: No such file or directory Installing app-text/gtkspell does the trick.
I do not think net-misc/modemmanager is shipping a /usr/bin/modem-manager-gui. Looks like a separate project that you have installed from somewhere (I can't immediately find it from Gentoo main tree). The only place I find this is in an overlay, which already has a gtkspell:3 dep in its modem-manager-gui ebuild, so I'm not sure what this is about. I suggest finding out where that modem-manager-gui comes from with this command: equery b /usr/bin/modem-manager-gui or: qfile -e /usr/bin/modem-manager-gui and then going from there.
Omg.. I'm so sorry for wasting your time. /usr/bin/modem-manager-gui was installed manually. =/ I'm not sure how you guys handle these mistakes by who reported, but you can delete this one for sure.
Alright. I guess it's a pity we don't have modem-manager-gui packaged then if it's useful to some, but that's a subject for other bug entries if interested (but preferably someone that's going to maintain it adding it via a pull request instead)
