Max,
there's an important difference between remote call control- and media-gateways.
The ESTOS CCG "software" provides remote call control functionality to control and monitor your PBX's system-phones.
To use the OC as a softphone it's mandatory to use a MS certified "hardware" media gateway ( (registration/configuration for this so called "Enterprise Voice" scenario is done in the mediation server) which supports the voice codec translation from your Aastra Box's world (TDM or IP) to the OC's codec. A media gateway we can recommend for the existing PBX world is e.g. the DMG 3000 from Dialogic. This works well in combination with the ESTOS CCG, also in more sophisticated scenarios with forking etc. .
Don't hesitate to contact ESTOS directly, if you need more information (info(at)estos.de) ,
regards,
CL, ESTOS GmbH