Off-hand, it sounds like your TA600R and the SIP are set up for different bandwidth. Does your TA have a menu option for "DS0 Maps"? If it does then go into "Edit/View Map1" area and see if the correct channels are mapped to the "TA IAD" or "TA600R". The default configuration only has DS0 24 mapped, so if you have a full T1 then you will have to map DS0s 1-23.
The IP addresses and subnet masks can be configured under Router > Config > Interfaces. You should see both the Ethernet interface as well as the T1 Interface, which should indicate it is PPP.
I'm afraid I'm not familiar with the terms "AR Serial" and "CR Serial" so I don't know which interface should be configured with them. The PPP interface is your WAN (wide area network) interface, though.
Hope this helps,
It did help thank you. Unfortunately not much of a change, however I am one step closer to what needs to be accomplished. As silly as this may sound there are two types of configurations for the 600r, remote and host router - which to some extent I assumed I was the remote router considering the ISP was accessing me, but I may be wrong. I've done both configs to no avail. With that said, does the Test and Turn up test from the ISP have to be active for me to see if PPP can be established or is this something I can know before hand? I've followed the config guide for the TA IAD, but still nothing - im assuming this is human error on my part.
T1 interface is configured to PPP, BZ8S, ESF, timing mode is Network, with no alarms and all values are 0 under status>performance> current and totals (which I was told was a good thing)
DS0 are mapped 1-24 at TA-IAD and router 64k
Router> T1 interface has Local ip address and Far End ip address inputted per ISP info, the WAN IPv4 addresses that were given to be specific. (however given the use of CR Serial INt and AR Serial INT, these could be backwards). Along with ip netmask set as WAN Link Subnetmask per ISP info.
Router> Ethernet Interface> primary ip is set given IP address by ISP.
Hopefully I'll be getting a call back from Adtran or AT&T - one of the two would be great. Again thank you for your response, its much appreciated.