VOIP Hosting

Hey guys I have a remote linux server. I want to put some kind of VOIP software on the server. Being able to share screens would be a plus or other productive bonuses like sharing files.

Have you searched for such software for linux using googlefu?

I have decided I wanted to use Teamspeak3 for now but while using this guide
https://www.digitalocean.com/community/questions/setup-teamspeak-server-ubuntu-15-04
the command sudo useradd -d /opt/teamspeak3-server -m teamspeak3-user responds with
sudo useradd -d /opt/teamspeak3-server -m teamspeak3-user
have any ideas?

Did you mkdir /opt/teamspeak3-server before you issued that command? You may need to use sudo or su if you don't have permission.