I have long wondered why, in the UK at least, abbreviated call-signs (on the radio) use the "G-" nationality identifier as the first letter.
Example: G-ABCD becomes G-CD
Practically every GA aircraft starts with G and as a result, call-signs do not really > stand out.
1) GA is international (at least it used to be until EASA started to mess things up). In Norway summer time we have piston singles and twins from all over Europe, especially from Germany and Sweden.
2) Back when I worked within ATC, the regulations were like this:
Station calling ATC uses full call sign on first call
ATC (who has information about other stations in the area) can (normally does) abbreviate the call sign if there is no conflict.
The pilot can abbreviate its call sign only after ATC has done so one time.
So, in other words, if you call ATC and they respond with your full call sign, you should continue using full call sign. In my time, I very often had pilots calling me using an abbreviated call sign on first call. Most times it was no problem.
EDIT: Eurocontrol ran a project to avoid call sing confusion and call sign similarity some time ago, however it was targeted towards commercial aviation.
