oops, I though I subscribed to this post, sorry that I didn't replied before. some asterisk features relies on 1000ms timing coming from zaptel PCI card or ztdummy. xen cannot share a physical card among virtual appliances (especially for timing!). ztdummy didn't seem to work out-of-the-box in virtual appliances and needed FIX. A long time ago, some guys tweaked it enough on Linux V-server to make it work at http://www.telephreak.org/papers/vpa/ callweaver.org (asterisk fork) kicked out zaptel timing, I didn't try it as a virtual appliance. I'm not tech enough to tell what, where, how to change zaptel. keep me informed, a PM to check if subscribing works for me.