asteriskのレポジトリを追加。
# vi /etc/yum.repos.d/centos-asterisk.repo

[asterisk-tested]
name=CentOS-$releasever – Asterisk – Tested
baseurl=http://packages.asterisk.org/centos/$releasever/tested/$basearch/
enabled=0
gpgcheck=0
#gpgkey=http://packages.asterisk.org/RPM-GPG-KEY-Digium

[asterisk-current]
name=CentOS-$releasever – Asterisk – Current
baseurl=http://packages.asterisk.org/centos/$releasever/current/$basearch/
enabled=1
gpgcheck=0
#gpgkey=http://packages.asterisk.org/RPM-GPG-KEY-Digium

# vi /etc/yum.repos.d/centos-digium.repo

[digium-tested]
name=CentOS-$releasever – Digium – Tested
baseurl=http://packages.digium.com/centos/$releasever/tested/$basearch/
enabled=0
gpgcheck=0
#gpgkey=http://packages.digium.com/RPM-GPG-KEY-Digium

[digium-current]
name=CentOS-$releasever – Digium – Current
baseurl=http://packages.digium.com/centos/$releasever/current/$basearch/
enabled=1
gpgcheck=0
#gpgkey=http://packages.digium.com/RPM-GPG-KEY-Digium

確認
# yum info asterisk18
インスト
# yum -y asterisk18

ひかり電話RT-200KIへのレジストの設定は後ほど。。。