Obviously I don't know how much e-Voice costs annually to run and I haven't added up the number of users but, setting aside the principle that it should be free to users, I am sure that the vast majority if organisations would be able to cough up (say) £25 or £50 a year to keep it going.
When the Essex and Surrey sites close, as they use the same technology I would anticipate that a fair proportion would migrate here, thus adding to income.