In Europe Eurocontrol from an ATC perspective have a project running to reduce callsign confusion.
The aim is where say an airline with callsigns AIRLINE-113 AIRLINE-123 and AIRLINE-133 all opereate in the same airspace then 2 will be changed.
Also they are looking at situations where AIRLINE1-333 and AIRLINE2-333 are also operating.
they are using a mix of alpha numeric callsigns and 3 or 4 digit to assist decluttering.
regards