Reporting back in case anyone else can benefit later...I got visual voicemail turned-off @ the carrier and this solved it! I DO get a notification when there's a voicemail awaiting and it goes away upon checking/clearing the VM box, but I no longer get the extra text messages. Mission accomplished - thanks @applee and @rocket2nfinity!

@antonyj Indeed, do not download the Anbox image on the Nexus 5. It is already pre-installed by default. Doing so might creating bugs.

Just start here:
sudo mount -o rw,remount /
sudo apt update
sudo apt install anbox-ubuntu-touch android-tools-adb
anbox-tool install
exit

If you have an error message telling you an insufficient memory in /var, you can try as following:

sudo mount -o rw,remount /
sudo rm -r /var/cache/apt # delete the apt cache; frees space on system image
sudo tune2fs -m 0 /dev/loop0 # space reserved exclusively for root user on system image set to zero
sudo apt update # recreate apt cache to install Anbox and adb
sudo apt install anbox-ubuntu-touch android-tools-adb
sudo mount -o ro,remount /
exit

So, after I dug out my old netbook from the dust of my stash shelf, which was already equipped with lubuntu 14.04, I successfully installed ubuntu-device-flash utility via apt package manager, and used the utility to downgrade to 15.04.

Wish, this can be this easy on bionic (18.04).

I will look into the ubuntu-device-flash utility on ubports github and try to make it work.

hey thanks 🙂

and i also just saw we now have Nexus section? 🙂

yay