System/Library/PrivateFrameworks/VisualVoicemail.framework/IMAP.framework

_VFBlockObservable.h

NSObject
>
VFObservable

@interface _VFBlockObservable : VFObservable {
    id /* block */ _block;
}

- (id)initWithBlock:(id /* block */)a0;
- (id)subscribe:(id)a0;
- (void).cxx_destruct;

@end