After the latest upgrade of the librem5-gnome-phone package, now apt says that haegtesse is no longer required:
purism@pureos:~$ sudo apt update && sudo apt upgrade
Get:1 https://repo.pureos.net/pureos byzantium InRelease [8733 B]
Get:2 https://repo.pureos.net/pureos byzantium-updates InRelease [4745 B]
Get:3 https://repo.pureos.net/pureos byzantium-security InRelease [4746 B]
Fetched 18.2 kB in 2s (12.1 kB/s)
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
All packages are up to date.
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
Calculating upgrade... Done
The following package was automatically installed and is no longer required:
haegtesse
Use 'sudo apt autoremove' to remove it.
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
purism@pureos:~$
The “apt show haegtesse” command says:
Description: A daemon to transfer audio data betwem a modem and PulseAudio
Some modems, like the SIMCom SIM7100 series, support transfer of
voice call audio over serial TTY devices. This daemon will sit on a
modem TTY port, wait for data and when it appears, transfer it to and
from PulseAudio streams.
Why is this no longer needed? Or was it never really used in the first place?
(Maybe @dos knows? 
)