I have found a way of getting ATC to identify third party aircraft,by their type as well as their call sign. thanks to "a1cpilot" for putting me on the right track. Here's how. The ui_ section of the aircraft.cfg file lets the sim identify the manifacturer, type and variation in the initial aircraft selection screen ( no more unspecified). The atc_ part of the [fltsim.0] section gives ATC your planes callsign and flight number, thus Concorde becomes "Speedbird 1".
To get ATC to call your plane Concorde or Grumman F14 you need to enter the details in the [General] section, not the [fltsim.0] bit. As follows
This set up means that when you change controllers or get in the way of another aircraft on taxi ATC calls the following:-
Rome center, Speed Bird 1 is type Concorde, request flight following.
For some planes there is only a type, Concorde, Sopwith and Schwiezer for example. Wheras others have different details for both. for example ATC will call the following Lockheed f16.
If these details are not put into the [General] section ATC calls your plane "experimental".
The atc_model line is a code, and it is not always obvious what it will be. For example 747-400 is "b744". It would be great if someone could produce a list of these codes. What for example is Sr-71a. I have tried SR71a, SR71 S71 ........
Anyway, I hope this helps and I'll stop going on about Concorde now !!!