I don't have an answer to your main topic/question- But just wanted to add: this sounds like an IA (Integrated Access) T1, rather than a classic Fractional T1. Which means there's a good chance it's actually VoIP. Most carriers nowadays use "dynamic" voice over a data T1 circuit, rather than fixed/static, or TDM based voice lines. This is because the 64Kbps normally allocated to an old static voice+data T1 is wasted when not used, VS. keeping the whole 1.5M available via dynamic voice, ie: VoIP (bandwidth is only used when a call is placed).

*Stand alone voice T1 or PRI does however use TDM, unless otherwise specified as a SIP T1.