[Asterisk-Users] more than one company hosting their PBX on the same machine?

[aakef at os-sp.com]

Did anyone try to have more than one asterisk installation on one machine?
Here's what i'm thinking, why can't amall and medium companies outsource their
telephony service to their data provider? So the ISP could offer a service to
its clients where it hosts the servers that run asterisk at their own premises
which is usually a suitable environment for hosting servers(UPS's and very good
network connectivity).
Summary: Is it possible to have more than one domain(as in the extensions don't
know each other) on the same machine? If it is, any recommended solutions? Many
virtual machines and each one has one asterisk installation? One linux box that
has several asterisk installations? What would be the hardware requirements for
running such a setup?

Regards,
Akef