I spoke with my counterparts over at NS last week on a different issue and we were comparing notes (BSing) on other comms stuff.
Right now there is NO practical way to use anything other than analog - for mainline and some yard operations.
As stated well before, there is no user friendly or practical way to handle certain railroad operations. Yes it can and has been used for yard specific functions, but those functions are generally limited to the car department, engineering, mechanical and the such. Those departments can use it successfully due to the fact they are not operating certain RR functions that TE&Y require.
NS also has a sizeable fleet of ASTRO Spectra RR radios still in locomotives (as does CSX) and older GE radios that are not NXDN/IDAS compatible and need to be replaced.
CSX, CN, CP, KCS all have sizable fleets of cab radios that are not compatible. To run interchange or runthru, the radio must be AAR compliant - and most railroads will not go and replace the radio or the lead locomotive unless cab signals or LSL is required.
Futhermore, as touched upon above, a few companies are still trying to come up with a proper radio interface with NXDN selcodes to operate such devices to be used. These devices currently run on DTMF signaling, and railroad are not going to install CTC along main just for a dispatcher to throw a switch once a week due to sheer cost.
What C&S tells me, integrated TDD's with NXDN haven't been offered yet, as they have been using in house radios. It would be easy to use an off the shelf radio, but then again to use recall codes, your back to trying to use digital SelCall to bring them up for a TDD recall.
This is why the AAR in the committee has essentially backed off on any use of digital radio when everyone was doing the digital craze years back. The committee never fully explored the ramification of the infrastructure costs.
Since then, most railroads (major ones) have bought NXDN compatible radios for locomotives, TE&Y, vehicles as part as the replacement cycle and failure of radios in the field.
Two of the Class 1's I work with have been buying the Kenwoods - one with custom firmware (which has had issues in the past) and one just preprogrammed with the full AAR analog and digital channel numbers (as well as custom zones for the intended area in service).
So, way in short, don't plan on seeing it on the main line for a very long time on the major railroads.
