We remain hopeful that these two tweaks will encourage Sangoma, the new owner of the Free PBX project, to do the right thing and get the non-commercial pieces of the project back on the right track moving forward.
As we’ve stressed all along, we do not want to tarnish the incredibly hard work that dozens of developers in the open source community have poured into both of these projects over the past decade.
We continue to be amazed at what they’ve been able to achieve, and we salute their accomplishments.
(None of the subsequent commands you recommend require the Software Center, nor do any of them use it or benefit from it if it's installed.) Note also that it seems unlikely this will keep the "packages can be updated" message from appearing.
If you have just added a PPA and have not updated, nothing from the PPA will work at all as you do not have a package list from that PPA or repository.
In particular, it would be cool to have a convenient, automated/automatable way to just install security updates, even when other updates are available and the software sources for them are enabled.
This error may occur if an attempt to run more than one package management process is made.
For example, if a package is being installed or removed using apt-get, or dselect, it should not be possible to run another package management tool, until the package updates are complete. Apt Pinning if you want an unstable package on a stable Debian system.