Trasncription from http://www.soft-switch.org:

"Unicall is an abstraction layer, making telephony applications largely independent of the protocols used to signal and transport phone calls. It consists of a very simple library, which is called by the telephony applications, and into which telephony protocols are plugged."

Currently it is the only free source channel to provide MFC-R2 signaling trunks, therefore its wide application in Latin America and Southeast Asia.

Original site and download for Asterisk 1.2: http://www.soft-switch.org.
Fine tutorials and download for Asterisk 1.4: http://www.moythreads.com/wordpress.
Download for Asterisk 1.44: http://br.geocities.com/bruno_agostinho.

Install procedure:

cd /usr/src
wget -c http://www.soft-switch.org/downloads/spandsp/spandsp-0.0.3.tgz
wget -c http://www.soft-switch.org/downloads/unicall/unicall-0.0.3pre11/libmfcr2-0.0.3.tar.gz
wget -c http://www.soft-switch.org/downloads/unicall/unicall-0.0.3pre11/libsupertone-0.0.2.tar.gz
wget -c http://www.soft-switch.org/downloads/unicall/unicall-0.0.3pre11/libunicall-0.0.3.tar.gz
tar xvfz spandsp-0.0.3.tgz
rm spandsp-0.0.3.tgz
cd spandsp-0.0.3
./configure
make
make install
ln -s /usr/local/lib/libspandsp.so.0 /usr/lib
tar xvfz libsupertone-0.0.2.tar.gz
rm libsupertone-0.0.2.tar.gz
cd libsupertone-0.0.2
./configure
make
make install
ln -s /usr/local/lib/libsupertone.so.0 /usr/lib
tar xvfz libunicall-0.0.3.tar.gz
rm libunicall-0.0.3.tar.gz
cd libunicall-0.0.3
./configure
make
make install
ln -s /usr/local/lib/libunicall.so.0 /usr/lib
tar xvfz libmfcr2-0.0.3.tar.gz
rm libmfcr2-0.0.3.tar.gz
cd libmfcr2-0.0.3
./configure --prefix=/usr/local
make
make install
cd asterisk/channels
wget -c http://www.soft-switch.org/downloads/unicall/unicall-0.0.3pre11/asterisk-1.2.x/chan_unicall.c
wget -c http://www.soft-switch.org/downloads/unicall/unicall-0.0.3pre11/asterisk-1.2.x/channels_Makefile.patch
patch -p0 <channels_Makefile.patch
cd /usr/src/asterisk
make clean
make install
cp channels/chan_unicall.so /usr/lib/asterisk/modules/
cd /etc/asterisk
wget -c http://www.soft-switch.org/downloads/unicall/unicall-0.0.3pre11/asterisk-1.2.x/unicall.conf.sample
mv unicall.conf.sample unicall.conf