I've noticed an increasing amount of clubs applying for heir own callsign and then giving each instructor and member a number.
This solves the problem of abriviation, callsigns are never duplicated, and pilots who fly many different aircraft don't get their callsigns mixed up (I know I've done it!).
The ATCO's I've talked to prefer it.
Although still mainly used only by commercial FTO's, company calsigns are getting ever more popular in GA.
Other advantages include:-
Being able to supplement the callsign with a letter such as 'T' to denote a skills test, or 'S' to indicate solo student.
ATC will know wich company an aircraft is with, which helps parking alocation and billing.
Local ATC will often get a good idea of pilots experience by there callsign: i.e assign 01-09 Instructors, 10-29 solo students, 30-69 PPL, 70+ IMC or IR.
I've flown using reg and company callsign, I much prefer the later.