Hello, I'm a voip tech with over 10y experience working for a US company on the level2/NOC department, I can install, troubleshoot and customize many SIP devices including softphones, ATAs, Ip-phones and PBX systems such as Asterisk/FPBX. I read your project description and I can help you fix that problem, doesn't really seem to be related with Asterisk but with the dial-plan, so I suppose it's better to use the server with the newer Asterisk version. You may contact me at any time.
Thank you.