Actually,
I've got exactly what your looking to do working perfectly. However, it's not. easy.
First of all. Where is the CallManager located? On a Private Network space? or Public IP address?
Either way, you must understand how the call setup process works. Once the IP Phone or SoftPhone registers with a CCM, it registers with its IP address. Then, whenever that Phone wants to call another phone, it makes a direct call to the other phone.
In my scnerio, I have 5 friends. All of which have IP phones at their House behind a Linksys Router, etc... We all have private IP addressing ( 192.168.x.x).
the CCM is @ my house. I have my Linksys setup to forward the ports (tcp and udp ranges) directly to the CCM, however, after the initial registration, the IP phone at House X that needs to call House Y, makes a direct call. Since we're all registered with non-routable space on the Internet, the packets are dropped at each other's ISP.
There are severa solutions to consider to make this work. One, try and keep some sort of Security, and yet, still register with a CCM with Private IP address, and still be able to call each other's houses.
I then thought, about making a GRE tunnel between each others houses. This of course, requires us have a cisco router at each house. We create a GRE tunnel between each house, and create static routes to each others network. once we did this, it didn't matter if we had private addressing or not..
example:
CCM= 192.168.10.20
House A = 192.168.1.x
House B = 192.168.2.x
House C = 192.168.3.x
House D = 192.168.4.x
Once the GRE tunnel is up between each house, we are now able to Ping each others "private" address space and keep our IP phones connected to the CCM. works great!
If anyone likes, I've drawn out a doc on how to do this on private addressing at home.
tony
