Some VoIP-hardware to play with: A Grandstream budgetone 101. First working call happened in 5 minutes from opening the box (calling my own speaking clock). The rest of the configuration took a bit longer.. I uploaded and configured the CTU ringtone from '24' as ringtone 1. One thing that does not work (and bugs me) is calling an xs4all number via asterisk: there is just no incoming audio data. Codec problem? Nat problem? No idea.