For such a a solid package so far the results have not been kind the the upgrade. Error after error, including development core needed, Zaptel manually compiled and more. So far I do NOT recommend the upgrade remotely. I see many issues , especially since the upgrade contained 368 programs and their dependencies, more than I expected.
I personally recommend always backing up your data and config files, and them do the update on a test bed. 2.0.2 upgraded without any issues, while 1.2.3 has nothing but. Seems one had a much more limited core base, so you have to install all kinds of rmps' or upgrades.
Can it be done without issues? So far the 4 or 5 links on google say no. All report all kinds of issues. After reading the upgrade details, I see where most would reboot and then issues would mound, since no modules come preloaded. Once you add your modules you can restore your previous services and routes, with few changes. Again backup your stuff.
value - medium to high - based on risk and changes
learning curve - extreem
alternative solution: download ISO and upgrade onsite
Have a CD packed with every package you need downloaded all at one time, at your finger tips, makes the install much smoother. Can you mangle your PBX ? Definetly. I run both servers and see 1.2.3 machines still functioning perfect for a local private phoner system deployable over the Internet, with software , time, more time, and patience.
Is it worth it ? 1000 percent. I love the new interface and more packages and options. I was able to hook the system into our prerecorded shows and demo our gabcast station.