iaxmodem software package provides software modem with IAX2 connectivity, you can install in your Debian 9 (Stretch) by running the commands given below on the terminal,
$ sudo apt-get update $ sudo apt-get install iaxmodem
iaxmodem is installed in your system.
Make ensure the iaxmodem package were installed using the commands given below,
$ sudo dpkg-query -l | grep iaxmodem *
You will get with iaxmodem package name, version, architecture and description in a table
| Distro | Debian 9 stretch |
| Section | Communication Programs |
| Package | iaxmodem |
| Version | 1.2.0~dfsg-2+b1 [s390x], 1.2.0 |
| Description | software modem with IAX2 connectivity |
| Sub Section | comm |