[asterisk-users] multiple PBXs in one box

[Joao Pereira]

Hello
I would like to know if it is possible to have multiple PBXs implemented 
in one Asterisk box.
I have different companies using my Asterisk server (remotely) and I 
don't want them to be calling each other.
I want to create different profiles in which my clients can only see its 
own PBX.
Each PBX will have its extensions and outbound/inbound routes... but 
everything in only one Asterisk.

Is this possible? How can I implement it? Creating different contexts?
Should I use a special software together with Asterisk?

Thanks
Regards
Joao Pereira