I downloaded the AsteriskNOW distribution and selected FreePBX. Later I used
yum to update the system including Asterisk and the FreePBX update features in the frontend.
The Asterisk-related help at sipgate basic Hilfe is not yet very detailed, but it was sufficient to get a working setup. Especially the remark about the change in type for Asterisk 1.6 is crucial and helpful.
Now it’s time to look for economical hardware running Asterisk and I am not talking about appliances, since I want to install a customized Asterisk/FreePBX on my own, recommendations are welcome.