the best way is to replicate Users from AD via LDAP ;)

Alternative you are able to put configurations via URL Command or XML Import to the PBX.

You can read some stuff about command handling here: http://wiki.innovaphone.com/index.php?title=Howto:Effect_arbitrary_Configuration_Changes_using_a_HTTP_Command_Line_Client_or_from_an_Update

XML Import (You must simulate the HTTP Request)

Example URL Command (Create new user):

https://<ip>/PBX0/ADMIN/mod_cmd_login.xml?cmd=submit-object&tab-active=&repsrc=&search-grp=&text=&cn=username&dn=&h323=username&e164=1337&email=&pwd=pass&pwd1=pass&node=root&loc=PBX&fake=&obj-url=&gi=&config=&no-devs=update&dev1.hw=&dev1.text=&filter=&cd-filter=&cfnr=&busy-out=&uc=&messages=&apps-my=&gw.name=&gw.ipei=&gw.dsp=&gw.ac=&gw.subs=&gw.fc=&gw.cki=&gw.ciph=&gw.end=.

You can modify as you need, but please note that the passwords/informations are not transmitted encrypted.