I looked at the Data Sheet for the Tandberg 6000 MXP and it looks like the device is a true H.323 endpoint.
Technically you could register this to Call Manager directly as an H.323 client. I have done this with other clients such as Microsoft Net Meeting etc. and they seem to work fine.
The only issue with not having a Gatekeeper in the mix is that you loose some of the zone management & QoS features that can be applied through the GK.
I did notice in the 6000 MXP Datasheet that is supports Call Manager integration with a Tandberg product called ECM? I have never heard of that product nor could I find any documentation on it.
As a side note, Tandberg has a complete line of SCCP or "Skinny" compatible devices that can register to Call Manager using the SCCP protocol instead of H.323. Essentially these devices look like IP Phones.
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