Do you mean a Cisco 675? (ie. the box they bought from Netspeed and improved some until it got unmanagable to update the code anymore?)
If that is the model, you can't hook up any ADSL device back-to-back to talk to one another, so no, you won't be able to do that.
At the other end of the DSL line at the CO would be a DSLAM, with line cards that can operate as the CO (ATU-C) side of an ADSL line which is required at the other end of the CPE (ATU-R, ie. what you have) to talk to one another.
If you have an SHDSL (ie. Cisco 828) or SDSL device, you could hook them up back-to-back, as SHDSL and SDSL devices let you choose one that can act as the CO end, and one as the CPE end.
Actually, quite a number of DSL units can do this, so you might want to shop around. I think there are whole neighborhood networks built this way, and you can also sometimes use alarm circuits (dry pairs) if you can get them.
I think you will find that most telcos have cleverly engineered the placement of load coils and frequency cutoff filters onto their "dry pair" circuits to thwart exactly this type of usage. If you try to order a dry pair for alarm signalling, that's exactly what they'll give you... a circuit that will pass DC and not much else. The one we initially tried wouldn't even pass voice. If by chance you get one, there's no guarantee it will continue working.
The telcos got wise to this circumvention of their tariffs back in the late 1990s and most of them nailed the door shut. If you want a "high speed" circuit, expect to pay for it.
You tell them all you want is a dry, unloaded copper circuit from point A to point B and they will tell you they do not have a tariff for something like that. If something isn't in the tariff base, they won't provide it.
My understanding of this is that the issue is bandwidth and levels. Because each telco circuit shares a common cable bundle, certain frequencies and unregulated subscriber levels can cause disturbance and disruption (interference) to other legitimatly tariffed services within the cable bundle. I know this to be true because I've seen the effects firsthand of trying to run ADSL in the same binder group with a 2-megabit E1. The E1 wins and the ADSL customer's throughput falls to practically zero.
I agree. But I would add that a lot of telco lines are coming out of an RT or remotw terminal, which may be down the block. The link from there back to the CO is fiber. So if you ask for a 'dry pair' for an alaro circuit, what you get is a pair that will have battery to sense the contact closure locally, and somewhere on the other side of the fiber link, the contacts of a relay will close. But in between all there is, is light.
The techs usually say that the DSL lines disturb T1 circuits, so they won't put DSLs in the same binder group with T1s. But it would make sense that the disturbance is mutual. It's just that T1 is all or nothing, whereas DSL can downshift to a lower speed and squeak by somethimes.
DSL lines were 'more better' in the beginning when there were a lot fewer, but as time goes on and more and more DSLs occupy the same cable and cause noise pollution to each other, the situation becomes 'worser and worser'.