No, sorry, I don't have any information about long-distance rates for other companies. I'm talking land-line here, and my basic service is with Bell, though I am signed on with another carrier for regular-voice long-distance calls. Frankly, now that I have the CI, I don't need to use the TTY as often. However, like you, I'm still inclined to use TTY for "formal" or business-related calls.
I suppose every carrier would set-up their own rate scheduled. A discount on a TTY call is reasonable, as the typing does take longer than voice communication, making the call last longer than it otherwise would. Don't forget you've got the VCO option with the Uni 1140, so when you are speaking with a hearing person they can at least hear your voice directly!
BTW, lisa ... prob. doesn't need mentioning, but hopefully the CHS rep explained that ADP will cover 75% of the cost of a TTY phone, provided you get a recommendation from your doctor.