Have seen numerous examples of similar callsigns in my little patch and I realise that sometimes it is unavoidable.
What really bothers me is there appears to be no real attempt by AsA, CASA or the airlines to try and minimise the risk.
Example: Two weeks after attending a briefing about this very subject, a well known regional carrier commenced a revised schedule which saw two of there aircraft, with similar callsigns (ie. 4643 and 4634) on a one-way route, passing nose to nose.
Throw in 3 or 4 other callsigns from the same operator, a busy evenings traffic, some WX diversions and multiple level changes and it's only a matter of time till something unpleasant
happens.