Thanks coppice , I couldn't find the (4 x E1 or 4xT1) on rowetel, would you place a direct link in here.
Also I want a complete open source VOIP system, we can run the asterisk on the beagle bone black, so now what will remain is the open source VOIP phones and Telephony Cards for connecting analog and VOIP phones to the system,
Is there an open source VOIP phone too?